FactionID

These are unique numeric identifiers for factions. They can be obtained for factions displayed in the player's reputation pane by calling the GetFactionInfo API function, or for any faction from the tables below. These values can be passed to the GetFriendshipReputationByID API function in the case of single-NPC factions like Nat Pagle or Gina Mudclaw, or used as a locale-independent way to identify factions in addons.

Top-level headers
The "Inactive" header does not have a factionID, but can be identified either by assuming it is the only faction or header without a factionID, or by matching its name to the FACTION_INACTIVE global string.

Faction NPCs with their own reputation
Rather than "reputation levels" these NPCs have "friendship levels".

Garrison Bodyguards with their own reputation
Rather than "reputation levels" these NPCs have "friendship levels".