What is a three-state circuit?
Normal push-pull outputs drive the output either high or low by turning one of the output transistors on and the other off. Tri-state outputs can turn both transistors off, effectively cutting off the output completely. This allows another output on the same wire to drive it either high or low without creating a short circuit between chips.

Tri-state outputs can be implemented with either BJTs or MOSFETs, so there is no direct relation between them and CMOS.