What is the JavaScript execution context?

An execution context is the environment in which JavaScript code is evaluated and executed. There are three types: Global Execution Context (GEC) — created on page load; the default context; creates the global object (window in browser, global in Node) and sets this to it. Function Execution Context (FEC) — created whenever a function is called. Eval Execution Context — rarely used. Each execution context has: a Variable Environment (all var declarations and function declarations, hoisted), a Lexical Environment (current scope + outer scope reference), and a binding for this. Contexts are managed by the call stack — when a function is called, its context is pushed; when it returns, it is popped. The outer environment reference forms the scope chain. Understanding execution contexts explains hoisting (variables/functions are processed before code runs within each context), closures (inner contexts reference outer environments), and this binding.