The "hash" is actually a "double-hash"... They do it twice, per problem.
SHA256(SHA256(x)) = (This hash)
The RATE = The number of those... per (second/minute/hour/day)...
EG, 600,000,000 hashes/s = ~0.00055THs, ~0.559GHs, ~572MHs, ~585,937KHs
http://egret.net/kb__mb.htmHashes / time = hash-rate
600,000,000 hashes done... took 3 seconds = 200,000,000Hs = ~191MHs
It is a rough estimation of the "ability" to process "hashes", which are the majority of the workload of the processing of blocks. Other things happen too, but that is the most dramatic, for processing.
It shows two things... The speed of the code used to process, and the speed of the cards ability to use that code to process. (Faster code processes faster, as does a faster card. "Diablo" is slightly faster code, in some instances, over "poclbm".)
