IVs are entered in steps, i.e., some before others
Interpret: R2 change, F change
Forward
The software enters IVs one by one until there are no more significant IVs to be entered
Backward
The software removes IVs one by one until there are no more non-significant IVs to removed
Stepwise
A combination of Forward and Backward MLR. Stepwise regression will do the most efficient job of quickly sorting through many IVs and identifying a relatively simple model based only on the statistically significant predictors.
Forward, Backward, and stepwise regression hands the decision-making power over to the computer which should be discouraged for theory-based research.