gate drive strength
The symbols, 1X, 2X, 3X...etc in an ASIC flow in used for convinience. What it means is a gate with 2X drive strength will have the same rise/fall time while driving a capacitance of 2C farads as that of a gate with X drive strength driving a capacitance of C farads. You can look at the schematic and see that gates with 2X drive strengths have approximately twice the widths on output pull up/pull down trasistors as comapred to the same gate with 1X drive strength. Similarly definitions for 3X, 4X etc.
This is to ensure that ratio of width to load capacitance remains constant, thus resulting in the same transition times. It is desired that the transition times in an ASIC chip be within a certain limit (DRV critereon). This will be met if the following rule is followed -
If 1X drive strength is sufficient to drive a load of C farads (ie, transition time is satisfactory) then 2X drive is satisfactory to drive loads between C farads and 2C farads, 3X drive is sufficient to drive loads between 2C and 3C farads....etc.
Hope this helps.