I think it's already in English: Underwriting Year. Little context here but it looks to me as if it is referring to the IBNR problem in long tail (re)insurance - so yes to your question. I.e. if you reinsure something like medical liability, it takes a long long time for all asbestosis cases to come to light. Therefore you have to make a large reserve for IBNR (Incurred But Not Reported) claims. As each year goes past, the actual reported claims for the year you accepted the reinsurance (the UY) will give you a better idea of what to expect (ie if you plot them on a graph and compare them with prior year experience you will see if you are higher or lower and what the ultimate outcome is likely to be).