WebAssembly is a binary instruction format for a stack-based virtual machine, designed as a portable compilation target for high-level languages like C/C++, Rust, and Go. Created through collaboration between major browser vendors, it runs at near-native performance by compiling to a compact, efficient bytecode that executes in a sandboxed environment. Unlike JavaScript, Wasm is statically typed with only four numeric types (i32, i64, f32, f64), enabling predictable performance and making it ideal for compute-intensive workloads like gaming, video processing, and scientific computing. The key insight: Wasm isn't meant to replace JavaScript—it complements it, handling performance-critical code while JavaScript manages the DOM and user interactions.