The University and College Union (UCU) is a British trade union. The union has around 116,000 members and is the largest further and higher education union in the world. UCU is a vertical union representing casualised researchers and teaching staff as well as "permanent" lecturers. Definitions of all these categories are currently rather grey due to recent changes in fixed term and open-ended contract law. In many universities, casualised academics form the largest category of staff and UCU members.