| We control what|
you think with
|Said and done|
|Jargon, buzzwords, slogans|
Gatekeeping is a term used to describe someone who is deciding on either the introduction of information to a particular body of knowledge or someone deciding on if somebody is a "real" fan of something, or even to restrict access to services. Sometimes the term is used more broadly, referring to any sort of superficial credentialism or stupid tests to deem someone "worthy" of discussing a topic.
Gatekeeping when used to scrutinize knowledge is perfectly acceptable for the scientific community when done in an objective way. For example, gatekeeping can keep badly-conducted science out of journals and financially/politically motivated science out of the general body.
On the other hand, in personal discourse, this can be as simple as someone saying "You're not a real fan of this!" based on knowledge of trivia.
Gatekeeping can happen when transgender people seek medical treatment to transition properly, but their doctor refuses to refer them to a specialist.