End-to-End Encryption
Encryption where only the communicating endpoints can read the messages, so the servers and providers relaying them in between cannot.
Concepts
Plain-language explanations of the ideas behind software - compilers, garbage collection, objects, types.
628 entries, all primary-sourced
Endianness
The order in which the bytes of a multi-byte value are stored or transmitted; big-endian puts the most significant byte first, little-endian puts the least significant byte first, a choice immortalized by Danny Cohen's 1980 essay.
Entropy (Information)
Shannon entropy measures the average information, or uncertainty, in a source in bits, and sets the theoretical limit on how far data can be compressed without loss.
Environment Variables
Named string values that a process inherits from its parent, such as PATH and HOME, forming a shared, inheritable configuration block carried through exec.
ETL (Extract, Transform, Load)
The pipeline that pulls data from source systems, cleans and reshapes it, and loads it into a warehouse; modern ELT loads the raw data first and transforms it inside the warehouse.
Event Sourcing
Persisting application state as an append-only sequence of events, so that current state can be rebuilt at any time by replaying the log from the beginning.
Event Streaming
Treating data as an unbounded, ordered stream of events on an append-only log that many systems can publish to and replay from - the model behind Kafka and modern real-time architectures.
Event-Driven Architecture
A style in which components communicate by emitting and reacting to events rather than calling each other directly, yielding loose coupling between producers and consumers.
Eventual Consistency
A consistency model in which, if no new updates are made, all replicas eventually converge to the same value, trading immediate consistency for availability.
Exit Status
The small integer a process returns when it finishes, where 0 means success and any non-zero value means failure, exposed in the shell as $? and the basis for error handling.
Extreme Programming
An agile software development methodology, created by Kent Beck in the late 1990s, that pushes good engineering practices to the extreme and relies on tight, continuous feedback from the customer.
Failure Detector
A component that suspects which nodes in a distributed system have crashed, usually via heartbeats and timeouts, and is inherently imperfect because a slow node cannot be told apart from a dead one.
Fault Tolerance
A system's ability to keep operating correctly even when some of its components fail, achieved through redundancy, replication, and failover.
Finite-State Machine
The simplest model of computation: a machine with a fixed, finite set of states that moves from one to the next as it reads input, and the exact device that recognizes regular languages.
First-Class Function
Treating functions as ordinary values that can be named, passed as arguments, returned from functions, and stored in data structures.
FLP Impossibility Result
A fundamental limit proving that in an asynchronous system where even one process may crash, no deterministic algorithm can guarantee it will always reach consensus.
Fly-by-Wire
A flight-control method that replaces mechanical and hydraulic linkages between the pilot's controls and the aircraft's surfaces with computers and electrical signals, enabling envelope protection and redundancy but making flight software safety-critical.
Foo, Bar, and Foobar
The canonical metasyntactic variables of programming, the placeholder names used in code examples to stand for anything; their etymology runs through WWII Army slang FUBAR, the Jargon File, and the deliberately whimsical RFC 3092.
Foreign Key
A column that references a primary key in another table, enforcing referential integrity so a row cannot point at data that does not exist.
Fork
Copying a project's full codebase to develop it independently, ranging from a permanent split off a project to the routine copy that precedes a pull request.
Formal Grammar
A precise set of production rules that generate exactly the strings of a language, used to define the syntax of programming languages so that compilers can parse them mechanically.
FOSDEM
The Free and Open Source Software Developers' European Meeting, a large free-admission gathering held in Brussels each year since 2001, organized by and for the open-source community.
Free Software
Software that respects users' four essential freedoms to run, study, share, and modify it; defined by the Free Software Foundation as a matter of liberty, not price.
Frontend State Management
The problem of keeping shared, synchronized UI state predictable as applications grow, and the libraries (Flux, Redux, MobX, Zustand, signals) built to address it.
Full-Text Search
Searching the actual text content of documents using an inverted index, with tokenization, stemming, and relevance ranking.
Function Composition
Combining functions so the output of one becomes the input of the next, written (f . g)(x) = f(g(x)); a core way functional programs are built from small pieces.
Function-as-a-Service (FaaS)
The compute model behind serverless: developers deploy individual functions that the platform runs on demand and scales independently, as with AWS Lambda, Azure Functions, Google Cloud Functions, and Cloudflare Workers.
Functional Programming
A programming paradigm that builds programs by composing functions and avoiding shared mutable state and side effects.
Functor
In functional programming, a type you can map a function over, such as a list or an optional value, transforming its contents while preserving its structure.
Garbage Collection
Automatic reclaiming of memory a program no longer needs, first put into practice for LISP around 1959 and 1960.
Glue Language
A high-level scripting language used to wire existing programs and components together rather than build systems from scratch, the central idea of Ousterhout's scripting thesis.
Godel's Incompleteness Theorems
Godel's two 1931 theorems: any consistent formal system rich enough for arithmetic contains true statements it cannot prove, and cannot prove its own consistency.
Good First Issue
A labeling convention, with the related help wanted label, that flags repository tasks as approachable for newcomers so that first-time contributors can find somewhere to start; on GitHub the good first issue label feeds discovery features that surface beginner-friendly work.
Gossip Protocol
An epidemic communication style where each node periodically exchanges state with a few random peers, so information spreads exponentially across a large cluster without central coordination.
Graph (Data Structure)
A set of nodes connected by edges, used to model networks, dependencies, maps, and relationships, and the substrate for a large family of algorithms.
Graph Database
A NoSQL model that stores entities as nodes and their connections as first-class edges, making relationship-heavy queries fast and natural without costly joins.
Greedy Algorithm
An algorithm that builds a solution step by step, always taking the choice that looks best at the moment in the hope that these local choices add up to a globally optimal answer.
Greenspun's Tenth Rule
Philip Greenspun's quip that any sufficiently complicated C or Fortran program contains an ad-hoc, bug-ridden, slow reimplementation of half of Common Lisp.
Hacker Culture
The playful, exploratory, meritocratic culture of programmers in which a hacker is a clever and enthusiastic builder, not a criminal; a tradition running from the MIT and Stanford AI labs through Unix, the Homebrew clubs, and the free software movement.
Hacktoberfest
An annual month-long event run by DigitalOcean since 2014 that encourages people to contribute to open source by rewarding a small number of accepted pull requests; in 2020 it triggered a flood of spam pull requests that forced the organizers to rewrite the rules around maintainer opt-in and quality.
Happens-Before Relation
Leslie Lamport's partial ordering of events in a distributed system: A happens before B if A could causally influence B; otherwise the two events are concurrent.
Hardware Errata
Documented defects in shipped CPUs and chips, collected in vendor errata sheets and specification updates, and worked around in microcode, firmware, or operating-system software rather than by replacing the silicon.
Hardware Virtualization (Intel VT-x and AMD-V)
Processor extensions, introduced by Intel and AMD around 2005-2006, that let a hypervisor run unmodified guest operating systems efficiently and safely in hardware.
Hash Collision
When two different keys produce the same hash value; unavoidable by the pigeonhole principle and handled by chaining or open addressing.
Hash Function
A function that maps data of arbitrary size to a fixed-size value, used for hash tables, checksums, and cryptographic security.
Hash Table
A data structure that maps keys to values through a hash function and an array of buckets, giving average O(1) lookup, insert, and delete.
Heap
A tree-based structure, usually an array-backed binary heap, that keeps the smallest or largest element at the root for fast access.
Heapsort
A comparison sort that builds a binary heap from the data and repeatedly extracts the maximum, giving guaranteed O(n log n) time in place.