WebAssembly (abbreviated Wasm) is a binary instruction format for a stack-based virtual machine. Wasm is designed as a portable compilation target for programming languages, enabling deployment on the web for client and server applications.
Wikipedia
WebAssembly (sometimes abbreviated Wasm) defines a portable binary-code format and a corresponding text format for executable programs as well as software interfaces for facilitating interactions between such programs and their host environment.
The main goal of WebAssembly is to enable high-performance applications on web pages, "but it does not make any Web-specific assumptions or provide Web-specific features, so it can be employed in other environments as well." It is an open standard and aims to support any language on any operating system, and in practice all of the most popular languages already have at least some level of support.
Announced in 2015 and first released in March 2017, WebAssembly became a World Wide Web Consortium recommendation on 5 December 2019 and it received the Programming Languages Software Award from ACM SIGPLAN in 2021. The World Wide Web Consortium (W3C) maintains the standard with contributions from Mozilla, Microsoft, Google, Apple, Fastly, Intel, and Red Hat.
As of December 2023, 99% of tracked web browsers (including mobile) support WebAssembly (version 1.0). But for older browsers, Wasm can be compiled into asm.js by a JavaScript polyfill.