Density dependent:
A limiting factor of a population wherein large, dense populations are more strongly affected than small, less crowded ones.

E.g. Emerald Ash borer on the ash trees in Ohio
E.g. Amount of food present in a given area for red fox

Density independent:
Density independent factors can affect a population no matter what it’s density is.

E.g. Rainfall (or lack of)
E.g. Tornadoes or high winds, which can kill entire tracts of trees