Joseki are "established stones" i.e. sequences of stones that are known to lead to a certain, balanced result. Most joseki concern attacks on a single stone in corners, although there are also joseki for attacking shimari. It usually described as a study not for amateurs, but for fairly advanced players.
The common proverb associated with the study of joseiki is: "Learning Joseki Loses Two Stones Strength - Studying Joseki gains four stones strength."
Ways of Displaying Joseki[]
Joseki can also be used to describe a time era of go, as in, "His joseki is very outdated." It may be used in that context, or it may be described as a game through multiple pathways in a book.