Premeditation is a rogue ability learned at level 30 for those with the Subtlety specialization. Rogues use it to generate 2 combo points on their target, which will allows them to use a finishing move faster.
Essentially, this enables rogues to gain 3 (or 4-5 if [Cheap Shot] is used) combo points from their opener alone.
Patch changes
/Patch 3.0.2 (14-Oct-2008): Premeditation (Subtlety) duration increased to 20 seconds, cooldown reduced to 20 seconds.
Patch 2.0.3 (09-Jan-2007): "Premeditation" (Subtlety Talent) has had its range increased to 30 yards.
Patch 1.12.0 (22-Aug-2006): Now instant cast with a 30-yard range. Old: 1 second cast time, 5-yard range.
Patch 1.6.0 (12-Jul-2005): Fixed a bug where the combo points gained using the ability were not properly removed after the duration expired. Also increased range and duration.