@babel/plugin-syntax-bigint enables Babel to parse BigInt literals (e.g., 123n). BigInt is a JavaScript primitive for arbitrarily large integers. This plugin only provides the syntax support, allowing Babel to understand the n suffix. It doesn't transform or modify the code, just allows parsing BigInt literals so they can be used in further transformations. A related transform plugin handles actual conversion for older environments. It’s crucial for projects targeting modern JavaScript features while maintaining compatibility.