In the chrome.storage documentation:

chrome.storage.sync.get(['key'], function(result) {
  console.log('Value currently is ' + result.key);
});

What is the value that is represented by result? My understanding is that it represents the object containing all key-value pairs in storage. But how does the function just "know" that this is what the parameter represents? I.e. aren't function parameters arbitrary and have values passed into them only when they are called?