by sculpting most people refer to Zbrush and/or Mudbox. Separate software that is used to sculpt a 3d model (base mesh or Z spheres). It's kinda like taking a brush and if you press it will model stuff in 3D - the different brush the different effect gained.
Units or keys depend on the NTCS or PAL system you want to combine your renders into. NTCS = 30 keys or frames per second, PAL = 25 keys of frames per second
Sorry to bother you, but I have a couple of questions. If you have time, I would like if you answer me By sculpting, do people mean pushing/pulling in paint deform. And, how many units of time in an animation make one second?