A type of causality
Used to describe a relationship between two events separated by distance in a temporal dimension. A causal relationship is one such that the occurrence of one event in dependent upon the occurrence of the other. Thus describing something a relationship as acausal means that the events in this relationship are not dependent upon each other. Describing a single event as acausal would imply that the event is not dependent upon any other event in order to manifest itself (I think this is impossible).
Causal--: I cut my finger ---> My finger bleeds
Acausal--: I cut my finger ---> The phone rings
Causality may refer to specific events in time or general trends among classes of events. The latter would be a statistical or probabilistic description. E.G. Cigarette smoke causes cancer.
Whether or not a relationship is causal or acausal, the property is not necessarily permanent for all similar relationships. That is, just because two events are causal once doesn't mean similar events will always be causal. E.G. If I buy a lottery ticket and win a million dollars, this is not necessarily repeatable.