Support
The portion of transactions that contain item set X.
This number presents how specific item set X is.
Confidence
The portion of transactions that contain both item set X and Y.
This number presents/estimate the conditional probability that Y exits when X exists.
Lift
$lift(X \Rightarrow Y) = \frac{supp(X\cup Y)}{supp(X) \times supp(Y)}$The ratio of the observed support to X and the assumption that X and Y are independent.
Conviction
$conv(X \Rightarrow Y) = \frac{1-supp(Y)}{1 - conf(X \Rightarrow Y)}$The ratio of the expected frequency that X occurs without Y.