Aloofness is a noun meaning a state of being distant, remote, or withdrawn. Someone showing aloofness might be shy, or just really doesn't want to be around people.
Aloofness is from the adjective aloof — originally a nautical term. The lee side of a ship was the sheltered side, but in a storm, if the wind was blowing your ship toward shore, you wanted to steer toward the loof (or weather side) of the ship, so that you weren't forced into the shore. Thus literally trying to keep your distance from shore by steering a loof, which gave rise to the more figurative meaning of being distant.