Acausality is being outside Causality, right? Causality is cause and effect, such as the the cause of being punched leading to the effect of being damaged, or the cause of someone casting a spell on you leading to the effect of you being mind controlled or whatever.
Acausality Type 5 is being outside Causality to such a level that you aren't affected by anything normally, so any attack or hax used on you won't actually change you in any way.
Also, Acausality Type 5 has been changed. Madoka who has only evidence of being outside a Tier 2 system of Causality is no longer unefefcted by Cosmic Armor Superman's 1-A stuff.
Acausality Type 5: