Raid Tokens are items that drop directly to the player's inventory for clearing various Raids. They always start out limited to one per week, and limits are lifted when a new Raid comes out.
The 8-player Normal Raids have a token only on the final floor of a tier, and either 7 or 4 of this token is exchanged in an Endgame Hub for an Allagan Tomestone Token. This Tomestone Token was then historically used alongside ten of a Rowena's Token, totaling a considerable sum (usually 1000) of Allagan Tomestones, to buy endgame weapons. This would allow players to save up Rowena's Tokens across several weeks to buy a weapon, given weekly Tomestone limits. However, as of patch 6.05 and the release of Asphodelos (Savage), Rowena's Tokens were discontinued. Currently, the Tomestone Token is used directly with Allagan Tomestones to buy endgame weapons.
The 8-player Ultimate Raids reward a token to each player upon defeating the final boss. These can be exchanged at certain vendors for Ultimate Weapons with three materia slots and special visual effects.
The 24-player Alliance Raids also have tokens, usually a coin, which are initially weekly-limited. However these are used to purchase Upgrade Items used to Augment Tomestone gear, improving its item level by 10 and making the gear dyeable.