Precog is short for both precognition, the ESP power to predict the future, and precognitive, someone with that power (or the adjective, as the case may be). Very short term precognition, for instance to dodge incoming attacks, is rather common among Package Deal Psychics such as Cavalier or Nex, and there are also a number of people with precog as a stand-alone power. The prevalence of precognitive powers among generalist espers/clairvoyants (of the non-package deal kind) is unknown.
Most precogs seem to see a spectrum of possibilities rather than just one definite future when looking more than a few seconds ahead, possibly because the future depends on the actions taken in reaction, but at least one person, Mrs. Potter, appears to be able to predict events days ahead on the other side of the world with astounding accuracy.[1] Comparing her to Chessmaster there is reason to believe that there may be an inverse relationship between how definite and accurate your predictions are and how hard you try to control the future, especially considering that Chessmaster appears to see accurate and definite predictions as the hallmark of lesser precogs.[2]
The ability to see the future several years ahead in at least very broad strokes seems to be reasonably common, though in the special case of mutant affairs there appears to be a block of some kind for predictions beyond 2008.[3] This was further researched by the MCO in the Report K4 and in the later Special Project Zulu.[4]