JSONP - Wikipedia

Under the same origin policy, a web page served from server1.example.com cannot normally connect to or communicate with a server other than server1.example.com. An exception is the HTML <script> element. Taking advantage of the open policy for <script> elements, some pages use them to retrieve Javascript code that operates on dynamically-generated JSON-formatted data from other origins. This usage pattern is known as JSONP. Requests for JSONP retrieve not JSON, but arbitrary JavaScript code.