HTTP
also: https, http method, http methods, http verb
The set of rules browsers, apps and servers use to talk over the web. Each message is a request asking for something, answered by a response.
The protocol for web requests and responses. A request has a method (GET, POST, PUT, PATCH, DELETE), a URL, headers and an optional body. A response has a status code, headers and a body. HTTPS is HTTP encrypted with TLS.
The script of ordering at a counter. You say what you want, and the staff reply with your order or "sorry, we're out". Both sides know the script, so any customer can use any counter.
Almost everything your app does online travels over HTTP. Agents describe problems in its terms: methods, headers, status codes. Knowing the basics lets you follow their debugging instead of just nodding along.
The form sends a GET request, so the data ends up in the URL. I'll switch it to POST and put the data in the request body.
Show me the HTTP request the checkout button sends and the response it gets back, including the status code.
Thinking HTTP and HTTPS are different systems. HTTPS is HTTP with encryption. Any real site with logins or payments should use it.