A JavaScript Promise is an object that represents the eventual completion or failure of an asynchronous operation. It allows developers to write cleaner code by handling asynchronous tasks more effectively, avoiding the so-called "callback hell." A promise can be in one of three states: pending, fulfilled, or rejected. When a promise is fulfilled, it means the operation completed successfully, and it can return a value. If it is rejected, it indicates an error occurred, and an error message can be returned. Developers can use methods like `.then()` and `.catch()` to handle the results of a promise, making it easier to manage asynchronous code.