You know about past and current events and the legends of the world. The topics you may know about include customs, inhabitants, laws, legends, personalities, traditions, founding of cities, migrations, royalty, and wars.
Synergy: 5 or more ranks in Knowledge (History & Current Events) gives you a +2 bonus to Gather Information checks. Also, 5 or more ranks in a Knowledge skill related to the topic being investigated gives you a +2 bonus to Research checks. These bonuses increase by +1 for every additional 10 ranks (that is, +3 at 15 ranks, +4 at 25 ranks, and so on).