Holodeck is the name of Star Trek Online's live server.
In STO all players are logging in to the same server. It has to be pointed out however that server only means one instance of server-side software. Actually Cryptic Studios maintains several physical computers that run the single server software.
Minor exceptions to the "one-server-for-all"-rule are the separate test server, where players can preview upcoming changes, and a number of in-house test servers for the development team.
 See also
- Tribble (server) for the test server.