'Combat detonations' ?

When you detonate a biotic or tech combo using a combat power detonator. Combat powers are the ones from single player on the combat tree. In multiplayer they are still represented as red even though there is no mention.

one of the easiest ways is playing with a priming ammo (indcendiary or cryo) and detonating with concussive shot (I beleive you need a evolution on the skilltree that allows it to detonate tho)

Concussive shot detonates combos at rank 1. More reason to leave it at rank 1 and spec rank 6 for everything else.

Except it's a great power to put five or six ranks into.

Trip Mine with 6a will detonate. But you're limited by grenade capacity. And the fact that it's a Trip Mine. Plus 6b is much better. I was thinking 6b in both Trip Mine and Barricade would prime for a Combat Detonation but this is good news. Concussive Shot spam will be much easier.