Any food (usually cake) left on the table of a communal staffroom of a large organisation where there is an unwritten rule that it is only for a certain group of people within the organisation.
Clique cake is a very common phenomenon in school staff rooms, where the cake in question is 'only for the Maths department' or other department.
Alternatives include cake being only for 'old timers' who have been at the workplace for over X years or 'you've got to know Bob to have a piece' cake.
'I wouldn't dare if I was you. It looks like clique cake!