Clairvoyance means "clear vision" and comes from French.
It describes generally the ability to perceive events and receive information without the use of the known senses. Information can be perceived at a great distance, and across time. Clairvoyance can be divided into several different subcategories.
Clairvoyance is best known where a clairvoyant tells about the deceased. Clairvoyants are also often asked for advice, when a house is alledgedly haunted.
So-called "clairvoyance meetings" are clearly different from seances. Here, the clairvoyant works with information, only in one direction. This means, one does not have the opportunity to ask questions "back". The clairvoyant acts as a kind of "channel" that transmits a one-way communication.
Another kind of clairvoyance - also called Remote Viewing - has been used extensively. During the Cold War, both superpower security services invested huge sums in Remote Viewing. Here a person, for example, got ordered to "see" what was happening at a particular coordinate.
The results were so convincing, that the US experiments first stopped in 1995 with a $ 20 million budget. The project was called "Stargate". It stopped officially due to the fact that spy planes and satellites turned out to be more economical.
It is not known how a clairvoyant receives and sends information. Seen with spiritual eyes, there is a direct contact with another world.
Scientifically, the abilities may perhaps be explained by the clairvoyant applying senses that not all humans have developed. Science know, we have many strange senses, and perhaps the clairvoyant has found out to drop connect to a sort of universal information cloud. However, this is purely speculative.