A power gamer is someone who primarily plays computer games that place particularly high demands on the hardware, requiring the latest graphics card and a fast processor. Commercially sold systems may be specifically advertised as being for "power gamers", as opposed to the cheaper and more common systems used in office computing. Typically, power gamers regularly upgrade their machines to include the latest hardware, in expectance of more demanding games and to get even better performance out of existing ones.
A power gamer (sometimes "powergamer") can also be a player of role-playing games who focuses on making their characters as powerful as possible; see powergaming.