Any url is a kind of complete address to some resource(file) in network. But according to the rules of how it must be actually (to work as you expect), its expected that a few characters must have some specific meaning; just like in this case: "/" means a separator that separates the individual elements of your address(url).
But in case you need such specific characters to be a part of any such element of address(url), we must encode it. List of codes
URL encoding converts characters into a format that can be transmitted
over the Internet.
- w3Schools
So, "/" is actually a seperator, but "%2f" becomes an ordinary character that simply represents "/" character in element of your url.
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