A statistical distribution is skewed when it has a longer tail on one side of the distribution. If the longer tail is on the left hand side, the distribution is left-skewed and has relatively more small values than large values. Otherwise if the longer tail is on the right hand side, the distribution is right-skewed and has relatively more large values than small values.

The following figures show distributions that are (a) right-skewed and (b) left-skewed.