Itemset

A set of items $X=\set{x_1,...x_k}$ used to find frequent patterns.

See Support, Association Rule, Confidence

Closed Itemset

$X$ is closed if it is frequent and there is no super-itemset with the same Support.

"Data Compression" of frequent itemsets.

Max Itemset

$X$ is a max-itemset if it is frequent and there is no super-itemset which is frequent.