Get:

With GET the form data is encoded into a URL by the browser. The form data is visible in the URL allowing it to be bookmarked and stored in web history. The form data is restricted to ASCII codes. Because URL lengths are limited there can be limitations on how much form data can be sent.

Post:

With POST all the name value pairs are submitted in the message body of the HTTP request which has no restrictions on the length of the string. The name value pairs cannot be seen in the web browser bar.

POST and GET correspond to different HTTP requests and they differ in how they are submitted. Since the data is encoded in differently, different decoding may be needed.