Initiative is one of the Attributes in Divinity Original Sin 2.
In D:OS2, Initiative is used to determine who gets to move first in battle. Note that D:OS2 is using a "round robin" system where no matter your Initiative, turns will always be taken in an alternating fashion between allies and enemies. Even if your 4-man party of allies has an initiative of 44, 43, 42 and 41 respectively, meeting a 4-man group of enemies with an initiative of 4, 3, 2, 1 respectively, the order of taken actions will be distributed evenly.
Using the above example of allies (A) and enemies (E), the order of taken actions would be: A44, E4, A43, E3, A42, E2, A41, E1.
What this means is that with initiative, you are only really deciding the order of movement and actions taken within a given sub-group, with little-to-no effect on how combat will play out. For all intents and purposes, initiative is largely useless, and should never be prioritized.