What does the white box in TAC display mean. There seems to be a white box in a red (enemy) infantry position near the target way point. What does it signify?

I have wondered that too, they are also just white boxes. I have looked while flying to see if there is anything there and haven't seen a thing.

Thought it might be a target area identifier or navigation point?

Grey are yet-unidentified objects. If it really is white then probably unclassified, but if you are seeing light yellow which it could be, then it's the player's targeted item.