Joseki 定石 are generally agreed-upon sequences of play. A joseki is a sequence of moves which results in what is normally considered a fair outcome for both players.
On the following pages, you'll find an extensive overview of joseki, a list of joseki pages and more thoughts about joseki, describing the thinking behind, the virtues and the dangers of joseki.
Here's already a quick reference:
Other initial positions are reflections and rotations of these points.