"Lore-friendly" term means that a mod is "canon compliant":
1)Does not contradict the source material. A Total War Warhammer lore-friendly mod does not contradict the history of "Warhammer Fantasy Battle" world (the tabletop game from which Total War Warhammer took inspiration). For example : adding skeleton archers unit to Vampire Counts is lore-unfriendly since there is no official sources that can confirm it (so it is an heresy!).
2)Is a logical extension of the source and game materials. For example: using bretonnian style models parts with vanilla textures (expecially legs) for some empire units or using different cultures/races models parts for a units (where possible).

Warhammer Fantasy World is full of history, tales and tradition documentations. Before using a "lore-friendly" mod you should be sure that the content is truly lore-friendly. This term is often abused from a lot of modders with a limited Warhammer Fantasy Battle knowledge. So be careful.... "All that glitters is not gold".

If you don't mind about lore, you wasted your time, just enjoy and play your Total War : Who Cares or Whatelse game.