One who has access to many administrative features on various servers of various different games. Server admins are saviors to some, but assholes to others. Some features include but are not limited to kick, ban, temp ban, burn, slay, teleport, freeze, switch teams, global chat. (these commands taken from various games)

Internet persona(s) who happens to follow you and you happen to follow them back and maintain communication with and have a mutual liking for eachother whether it be friendship wise, etc. (Mutuals if more than one mutual)

An administrator on an online game, who can do administrative things, like ban, tempban, mute, kick, freeze, jail, teleport any player. The role of an server admin(istrator) is to keep the server clean and safe for evrybody who is playing on it, punishing anybody who is doing things against the server rules, so it's usually has the overall control of the server.
In the most situation, server admin's username is highlighted or colored (usually in red or gold).

Sometimes an admin can be good with other server staff and players, but bad with some players (this is a special and probably rare case, and it may not happen on any server; this situation is usually found on servers with a lot of staff).