A Tactic Fragment is a Tome of Knowledge entry that contributes toward unlocking a Tome Tactic. Tactic fragments can be earned by talking to an NPC, killing a named mob, or maxing out a Kill Collector quest. A Tome Tactic is earned after collecting five or ten tactic fragments of a particular type and then purchasing the respective tactic from a Librarian.
An example of a tactic fragment follows:
Specific Example = The Hunger Pangs quest (a Bestiary Unlock) awarding a Beastial Tactic Fragment earned by killing about 50 salamanders and then talking to the kill collector (Dieter Stroh) at Felde Castle in Troll Country.