An MMORPG is a Massively Multiplayer Online Role Playing Game. These games once played with players in the same room on a simple board depicting a specific setting, have evolved into something far more complex and engaging, and able to accommodate many more players.
Star Trek Online is set in the year 2409 in the prime timeline, 30 years after the events of Star Trek Nemesis. However, it includes a few story elements that were outlined in the recent Star Trek film by J.J. Abrams. In particular the destruction of Romulus, and the disappearance of Spock and Nero.
After the destruction of Romulus, the Klingons have made a grab for territory which was originally theirs, and conquered several races on their way. The treaty of peace between the Federation and the Klingon Empire has broken down.