what is the request payload in jaavascript fetch

fetch('https://jsonplaceholder.typicode.com/posts', {
  method: 'POST',
  body: JSON.stringify({
    title: 'foo',
    body: 'bar',
    userId: 1
  }),
  headers: {
    'Content-type': 'application/json; charset=UTF-8'
  }
})
.then(res => res.json())
.then(console.log)

fetch('https://jsonplaceholder.typicode.com/posts/1')
  .then(res => res.json())
  .then(console.log)