Buff

A buff is a temporary beneficial affect placed on a player. Buffs can be dismissed by right-clicking on the icon.

Class buffs
Class buffs are long-lasting buffs that increase the combat abilities of group members. Every class have one. Because they can be unlocked across all characters, they are considered the baseline buff that should be on all the time, among the first things to be applied after revival.

Class buffs can be unlocked by completing Chapter 2 of the relevant class. Once unlocked, it will be applied to all your character's class buff ability. Class buffs are the same between matching classes across factions. Mirrored class buffs replaces each other and do not stack.

For example, after you complete chapter 2 of the Jedi Consular story, when you play a Sith Warrior your Unnatural Might ability will also grant the Mark of Power buff, because you have unlocked Force Valor, and Mark of Power is its mirror.

Galactic Republic

 * Jedi Knight: Xpbonus.png
 * Jedi Consular: Forcevalor.png
 * Smuggler: Scorelliannomad.png
 * Trooper: Touterrimveteran.png

Sith Empire

 * Sith Warrior: Swsithpureblood.png
 * Sith Inquisitor: Markofpower.png
 * Imperial Agent: Rushedshot.png
 * Bounty Hunter: Cyborgmerc.png

Raid buffs
Raid buffs are short-term group buffs that dramatically boost the combat ability of the team. Not all classes have them.

Because they have long cooldown and last 10 seconds, they are usually reserved for the burn phase of boss fights, to improve the group's chance to finish the fight before being overwhelmed.

Galactic Republic

 * Jedi Sentinel: Twilekvisionary.png
 * Jedi Sage: Forceempowerment.png
 * Scoundrel: Hotstreak.png
 * Commando: Suprechargedcelerity.png

Sith Empire

 * Sith Marauder: Predation.png
 * Sith Sorcerer: Unlimitedpower.png
 * Operative: Tacticalsuperiority.png
 * Mercenary: Suprechargedcelerity.png

Gunslinger's  and Sniper's  are also often considered a raid buff, but for defensive purpose and with more restrictions.

Many classes also have passives that increase the damage taken by the target. They are also sometimes referred to as raid buff, but for most discussions raid buffs mean the above abilities.