The Sight is the magical ability to perceive the supernatural. It is an inherent magical gift, though there are ways to induce the effect via certain methods like Fairy Ointment. Those who have it are often left able to not only see things that others can't, but interact with them in ways that others can't. While this is an incredible gift, it often causes trouble as it draws attention from apparitions and other entities and makes living with those who can't understand difficult.
Every magus can perceive the supernatural, as that is the means they draw their power. Sleigh Beggy like Chise Hatori not only perceive the supernatural, but draws them to her much more strongly. Aside from them, only a select few individuals have that ability, and the extent to which varies. Some can only perceive the fae that don't actively hide themselves, while others can see through even those.