Fodder literally means food for livestock. Figuratively it refers to random nameless soldiers who are plentiful in numbers but have no notable feats or skills worth noting. Basically these are the kind of characters who get stomped all the time by any named character. Although, fodder in some universes can be so much tougher than be far tougher than named characters from other (much weaker) universes (example, even fodder Space Marines from Warhammer 40K can be so far above named Harry Potter characters, then again just about everyone is so, shocker). Also named characters with no feats or reasons to be powerscaled can be considered fodder level (dependant on the context of the power levels of that universe)

Examples of fodder:

Stormtroopers (Star Wars)

Orcs (Lord of the Rings)

Imperial Guardsmen (Warhammer 40K)

Red Shirts (Star Trek)

Vehicons (Transformers Prime) (excluding Steve)

Firebender Troops (Avatar: The Last Airbender)