Acorn-loose is a tolerant parser for JavaScript, designed to handle non-standard or slightly broken code. It's built as a variant of the Acorn parser, relaxing some of its strictness to allow parsing code that Acorn would normally reject. This makes it useful for applications that need to analyze or process user-generated code or code that may not adhere perfectly to JavaScript syntax rules. While forgiving, it still aims to provide meaningful syntax tree output.