Kicker is an additional cost ability that can be found on many different cards throughout the MTG series. Kicker allows the creature and extra ability that can be played when it comes into play.
Most Kicker creatures have added abilities, like +1/+1 or a certain ability that will give it an edge. However, there are creatures with kickers that are pointless to use.
Multikicker is a creature ability that was released in the debut of Worldwake and appears and a few cards from the set. This ability allows the creature to use the kicker ability by paying it more than once. Remember, the multikicker ability triggers separately, so once 1 of it resolves, you can play the 2nd and so forth.