Clairvoyance is what most people think of when they think of psychics. In fact, for most people clairvoyant is synonymous with psychic energy.
However, in fact, this is actually only one of many different means by which people can receive information psychically.
"Clair" means clear while "voyance" is seeing. Therefore, the idea that it conjures up is that people who have these abilities are literally "seeing clearly". In other words they are receiving their information through visions, for example with their mind’s eye.