Not quite, my understanding is that a "round" is blocks found by Eligius pool. So if we find 2 blocks in a row, the round will be short. If we go several blocks without finding one, it will be a longer round.
E.g. at the moment, last block found by Eligius was #281910. Current block on the network is #281917. If we find block #281917 (actually, we just did), this "round" will be blocks #281911 - #281917.
In a basic PPS system, each share is worth a given BTC. Since we expect 1,789,546,951 shares = 25 BTC, each share = 1.397*10^-8 BTC. Every share that you put in is worth that much. However, you can't always get paid on those, because the pool doesn't always find the blocks. So your older shares get put on the "shelf" to get paid out when the pool is lucky. I am not sure where the cutoff is to be put on the shelf vs. being included in the current round. (I understand PPLNS better than I do CPPSRB, but I know that the Eligius system is pretty much the best / most consistent.)
I am also a newb, this is just my understanding, and I welcome any corrections.