Fodder enemies are enemies who have little health and barely damage the player. What they lack in strength they make up in numbers. Games like Dynasty Warriors boast the fact that they can have hundreds of enemies on screen, most of these enemies being fodder enemies. Thanks to their numbers, these kinds of enemies can overwhelm the player, chipping away at their health.
Fodder enemies are easily defeated. As stated above, they have little health meaning that a broad sword swipe or an explosion with large splash damage can easily finish them off. Fodder enemies all look the same, seeing how there are so many of them the developers usually only make two or three variations of fodder enemies.
Zombies are a type of fodder enemies despite the fact that they are not actively trying to kill you (they tend to only attack if you get too close). One zombie is relatively harmless, one well placed shot in the head usually deals with the walking pile of flesh. However a swarm of zombies (usually 30 to 50 zombies) can overwhelm the player by rapidly surrounding him and lunging.