regenerator-transform is a Babel transform that converts ES2015 async/await functions (and generator functions) into an equivalent but universally supported ES5 state machine. This allows older JavaScript environments to execute modern asynchronous JavaScript code. It's a crucial dependency for Babel users targeting legacy browsers or Node.js versions. The transform handles the complexities of regenerator behavior, ensuring correct execution of asynchronous control flow. It's generally used as part of a larger Babel configuration.