it means the precision at K(10) or precision for first 10 documents retrieved. In other words - number of relevant documents amongst retrieved 10(k) of them S

it means the precision at K(10) or precision for first 10 documents retrieved. In other words - number of relevant documents amongst retrieved 10(k) of them So 0.98 precision would mean that 9.8 out of 10 documents are relevant on average