Support: measures how frequently the collection of items occur together as a percentage of all transactions. How often do these things appear together?
Confidence: given that a customer purchased a set of items A, how often will they then purchase set of items B?
Lift: helps determine if combining a product with another improves the chances of making a sale (a lift > 1 indicates positive correlation: a customer who buys one item is more likely than average to purchase the other item as well).