What is the seated yoga position called?

You must be thinking of either the full lotus or half lotus positions. The full lotus is where both feet on crossed so that each foot is resting on the opposite thigh. The half lotus is where there is one foot placed on top, and one tucked under-neigh.

These are not it though. There is also Seiza, which is kneeling, and burmese, where one foot is placed on the floor, with the other placed in front.