A diamond spread is one of the terms many people do not understand. It basically refers to the face-up appearance of the stone, meaning a stone with a good spread looks larger than its carat weight suggests. That said, a flat stone is definitely not what you want, which is why the cut of the stone is very important here.
Most engagement ring shoppers seek out larger looking stones, but many fail to find one with the perfect balance of size and shine. This is one area where a shopper needs to be really careful because if they are not careful, the purchase could end up a disaster. Be sure of the cut grade, and check out the HD videos they let you watch before buying the stone. This should give you a good idea about how it would look on your finger.