Perception is the general ability to pick up on one's surroundings and notice anything of interest. It includes tapping into all the five senses, and some say those with a particularly powerful perception have been able to hone a sort of "sixth sense". The perception skill assists with detecting those who are hiding as well as assisting some particularly reflexive abilities. It also aids in the defense against things that are hard to see but are not wholly physical.
It is seriously hindered by wearing items that may hide the eyes, including deeply hooded cloaks and greathelms. However, with enough proficiency in armor use, this penalty can be reduced.