What are units in pensions' context? It seems such a basic term that I didn't find any site with a simple explanation for it.
Often pensions are invested in funds, or "unit trusts", that are denominated in "units". So each pension contribution you make will be going to buy a number of these units of a particular fund, which just means how much of it you own.
You should look for the unit price for the relevant fund to understand how much each unit is worth - it may not be explicitly stated as that, but it'll be the headline price for the fund.