Causal & Non-casual Systems
Casual System
Casual system is a system where the output $ y(t) $ at some specific instant $ t_0 $ only depends on the input $ x(t) $ for value of $ t $ less than or equal to $ t_0 $.
Non-casual System
Non-casual system is a system that has some dependence on input values from the future (in addition to possible dependence on past or current input values).