Pathfinder is an extension of Dungeon and Dragons 3.5 Edition and was developed after Wizards of the Coast butchered D&D with 4th Edition. Pathfinder is usually referred to as D&D 3.75 Edition. It has a wealth of source material and is a ripe setting ready to explore. It’s a great introduction to role playing games for all ages.
You can find out about Pathfinder on Paizo’s website.