Clock sink
Beginner
Any part of the chip that the clock has to reach.
Novice
An endpoint of the clock network: the clock input of a flip-flop, a latch, a memory block or a clock-gating cell. A block of a chip can have tens of thousands of them.
Expert
CTS balances arrival times at sink pins. Some pins are declared excluded or ignored (not balanced), and memory blocks and other macros can carry their own internal clock delay that CTS must account for.