CTS Terminology

• Stop (Sync) Pins: All clock pins of FF are called as Stop (Sync) Pins. The clock signal  should not propagate after reaching the syc/stop pin. This pin needs to considered for building the clock tree. 
• Exclude (Ignore) pins: All non clock pins such as D pin of FF or combo logic’s inputs are called as Exclude (Ignore) pins. These pins are need not to be considered during the clock tree propagation.
• Float (Implicit stop or macro model) pins: This is same as sync or stop pin but internal clock latency of that pin is taken into consideration while building the clock tree. Its a clock entry pin of hard macros and it needs to be considered while building the clock tree. But before considering this as sync pin, the macro’s internal tree needs to be balanced.
• Explicit sync (stop) pins: Input of a combo logic is considered while building the clock tree. Mostly this comes to picture  whenever clock gating concept is used.
• Explicit Exclude (Ignore) pins: Clock pin of a flip flop is not considered as sync/stop pin. This is also again due to the use of clock gating concept. Because while gating the clock, the clock signal will be given to an and gate.