A promise represents the completion of an async function. It is an object which will return a value. You can initialize a promise with "new Promise" syntax, and it is initialized with a function. Function gets passed to a promise has "resolve" and "reject" parameters, which handles the success and failure of an operation respectively. Example:-

// Initialize a promise:- const promise = new Promise((resolve, reject) => {})

// If we inspect the promise above, we would get:- proto: Promise [[PromiseStatus]]: "pending" [[PromiseValue]]: undefined

When a value is given to the promise:- const promise = new Promise((resolve, reject) => { resolve('We did it!') })

// Now we will inspect the promise above, we would get:- proto: Promise [[PromiseStatus]]: "fulfilled" [[PromiseValue]]: "We did it!"

As I had said, promise is an object that may return a value. After being successful it goes from undefined to being populated with data.