The basic premise is, instead of relying exclusively on the URL to indicate what webpage you want to go to (and just using the one method), it's a combination of VERB and URL.
This way, the same URL, when used with a different verb (such as GET, PUT, POST, DELETE), will get you to a different page. This makes for cleaner, shorter URLs, and is particularly adapted to CRUD applications, which most web apps are.
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