From 60ft6in.com:
CONTROL: ‘Control’ is the ability of a pitcher to locate his pitches. There are different levels of ‘control’. A pitcher may have poor ‘control’, like Bobby Parnell, which leads to a high walk rate. Or, there are excellent ‘control’ pitchers like Roy Halladay and Cliff Lee, who seem to dot the catcher’s mitt with every pitch. Then, of course, there is everyone else fitting somewhere in between.
COMMAND: ‘Command’ is the ability of the pitcher to make the ball move the way it is intended to move. For example, when a pitcher has good ‘command’, his curveball will always curve, his slider won’t “hang” and his 2-seamer will sink. ‘Command’ refers to the action of the pitch. There are different levels of ‘command’.