1. adj. Used of hardware or software designs, implies 'elegance in the small', that is, a design or implementation that may not hold any surprises but does things in a way that is reasonably intuitive and relatively easy to comprehend from the outside.
The antonym is 'grungy' or crufty.
2. v. To remove unneeded or undesired files in a effort to reduce clutter:
"I'm cleaning up my account."
"I cleaned up the garbage and now have 10 Gigs of freespace on that partition."