Someone who guards or monitors passage through a gate.
H.323 Gatekeeper, a computing term for a virtual network switch that manages a H.323 zone, providing address information/translation and other services to the terminals within the zone, and for Gatekeepers managing other zones.
A Gatekeeper can describe a person who picks the best news and forwards it to newspapers.
Gatekeeping (communication) involves the actions of persons or organizations, known as Gatekeepers, that manage or constrain the flow of knowledge and information.
Gatekeeping (education) the process of controlling the rate at which students progress to more advanced levels of study in the academic setting.