What to do when "it" is redundant? [closed]

You do not need to use full sentences when writing definitions. The implied subject is the term which is being defined, and the implied verb is an expression of equivalency (generally the verb is assumed to be "is"). You seem to already realize this in the first part of each definition.

HTTP: short for HyperText Transfer Protocol (http://).

Here you are allowing the term "HTTP" to serve as the subject, and leaving the verb (is) unstated. As long as your editor or instructor has not given you specific instructions to the contrary, you can safely leave the subject and verb implied for the entire definition.

HTTP: short for HyperText Transfer Protocol (http://). A protocol to see web pages, used by the World Wide Web to exchange data between your browser and a website.

Most dictionaries do not use full stops in definitions, so it may be better to use a comma or semicolon (as appropriate).

Also, be careful to be consistent. You have included the verb "is" in your definition of Google AdSense, but the equivalency verb should be left implied in a definition.

It may be helpful to spend a bit of time looking at the structure of entries in popular English dictionaries if you would like to gain a little more confidence.

Perhaps a simple rewording will work instead of specifically replacing "It is a"

HTTP: short for HyperText Transfer Protocol (http://), a protocol to see web pages that is used by the World Wide Web to exchange data between your browser and a website.

HTTPS: short for HyperText Transfer Protocol Secure (https://), a more secure version of the HTTP.

Google Adsense: an advertising program from Google, allowing publishers to display ads on website pages.

Website: a collection of web pages accessible via the Internet, also referred to as a "site" for short.