This cache page describes the difference between two common methods of sending data between a client and a webserver. I have kept it very high level so the description deliberately omits/simplifies a lot of information for clarity.
To view a webpage, you (the "client") make an HTTP Request to a webserver which then sends an HTTP Response with the requested data.
Often, you will need to pass additional information to the webserver - such as a password, a phone number, a search request etc... This is commonly done using webforms. Form data is mostly sent using two methods $_POST and $_GET
The $_POST method sends the input values to the webserver in the body of the HTTP Request. The webserver uses these values to decide which pages or which information to send back to the user in the HTTP Response. However, it doesn't send back the original input values. This means that if you try to resubmit the form, or click the "back" button on your internet browser, this information will no longer be available.
The $_GET method makes the HTTP Request in a slightly different way. The data is included in the URL (address bar) as a variable denoted by a "?" after the web address. As the value is part of the address, you can bookmark it, use it in links and it will be stored in your browser history. If you click "back" on your browser, the data is still available. You can also directly make manual changes to the data in the address bar. This makes it far less secure than the $_POST method.
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