Jison is a parser generator for JavaScript. It converts context-free grammars into efficient, readable JavaScript code that can parse input based on those grammars. It's ideal for creating custom languages, interpreters, or compilers directly within JavaScript environments, both client-side and server-side. Jison supports various grammar notations inspired by Yacc and Bison, ensuring a smooth transition for users familiar with those tools. It simplifies parsing tasks significantly, making complex syntax structures manageable.