Believed to be Customer Information Value, but there have been some variations. It is believed to enable staff to better assess who to up*rade or other similar commercial decisions, or who to offer what type of benefit (ie hotel grades) when delays occur.

It is all a bit mysterious, but does not or should not affect the service you receive as an individual - which in my experience is correct (particularly with my CIV!!)
Believed to be a way of differentiating between large numbers of BAEC card holders. As mentioned above, bigger score = more revenue for BA. I do CE full fare returns between LHR-LCA only, so am never going to get above Silver or have huge spends, but the regular CW TATL pax would have quite high spends and CIV.

Hope that helps, Any clearer?