A WASM file contains binary code saved in the WebAssembly format that is run in web browsers, such as Google Chrome, Mozilla Firefox, Microsoft Edge, and Apple Safari. It stores a module, which is binary WebAssembly code that has been compiled from C, C++, or Rust textual code, that can be imported into webpages and apps and used via JavaScript.

You can compile C, C++, and Rust languages into the WebAssembly binary format (WASM file) using various programs, such as Emscripten and WebAssembly Explorer. WebAssembly is useful because it is efficient, fast, safe, and can be debugged and tested. The format also allows you to integrate open source projects written in C, C++, and Rust into webpages and apps.