Warhammer Fantasy Battle or WHFB was a tabletop war game produced by Games Workshop and set in the Warhammer Fantasy universe. It was played on a tabletop using small plastic miniatures and a complex set of rules.
In 2015, the game was discontinued (presumably due to low sales, and/or a desire to create a more unique setting for copyright purposes). However many of the models are still produced and can be used in other games by Games Workshop.
When creating Total War: Warhammer and it's sequels, Creative Assembly looks to rules from this tabletop game to inform their decisions about how strong/weak etc a unit should be or what mechanics it might have.