Favored Enemy

Favored Enemy (passive): Favored Enemy grants +2 to damage and +2 to the skills bluff, listen, and spot against a specific creature type (chosen by the player). This feat advances by +2 at levels 5 and 10. One additional enemy can be chosen at levels 5 and 10. It also grants an extra +2 at levels 5 and 10. The following monster types are available to be chosen: Aberration, Animal, Construct, Dragon, Elemental, Giant, Dwarf, Elf, Goblinoid, Gnoll, Halfling, Human, Reptilian, Magical Beast, Monstrous Humanoid, Ooze, Chaotic Outsider, Evil Outsider, Lawful Outsider, Undead, Vermin.

For example a ranger is able to select Goblinoid as his favored enemy at first level and get a +2 bonus. At fifth level he is able to select [[Giant and he will get a +4 bonus to both Goblinoid and Giant enemies.  At tenth level he gets to select yet another class of enemy and the bonus on all of them increases to +6.