Causality
A system is said to be "causal" if at any given time, the output signal depends only on the present and/or past input signals.
A system is said to be "non-causal" if at any given time, the output signal depends on the future input signal.
As an example, the output signal $ y(t) = x(t+3) $ where $ x(t) $ is the input signal would be non-causal.
