The rooms in which poker is played, or the organizations who run those rooms. Most casinos that offer poker have a separate room, or at least a roped-off area, designated as the cardroom. In some places where poker is legal, you will also find separate cardrooms (not part of a larger casino) dedicated mostly to poker.
Cardrooms are the rooms in a casino or gaming establishment where poker is played. It can also refer to the organization that runs the games. Sometimes called poker rooms, when used exclusively for poker games.
A cardroom (also spelled card room) is a gambling establishment that exclusively offers card games for play by the public. The term poker room is generally synonymous, since the gambling games played in such establishments are typically, and sometimes exclusively, variations of poker such as Texas hold 'em.