Kayan is not a Quranic or Islamic name. It is a Persian word from Pahlavi sources and means "great king", "royal", "high status", "important person". Since the meaning is not bad Muslims can use it. It is a boy name, but Kayan is also used for girls.
Another name that sounds like Kayan is Keyan, which is a Quranic name. You can see its details here: Keyan