Convergent evolution is "the independent evolution of similar features in species of different periods or epochs in time".  A simple example is fish and dolphins.  Fish didn't just become dolphins.  First a non-fish became a fish, then they exited the water, then they grew legs, then they re-entered the water, then they lost their legs.  Both fish and dolphins became water-dwelling fin-propelled animals at completely different points in history and in different branches of the tree of life. 

Pretty much every section of that Wikipedia page made my jaw drop, but the part about light skin color evolving twice was pretty cool. #science