Every mining conversation runs on one unit. Machines are sold by it, networks are secured by it, and your revenue is a fraction of it. Here's hashrate, explained properly.
A hash is one attempt at the mining lottery: the machine takes a candidate block, runs it through a cryptographic function (SHA-256 for Bitcoin, Scrypt for Litecoin/Dogecoin), and checks whether the output meets the network's difficulty target. Almost every attempt fails. Mining is simply making attempts at a staggering rate — and hashrate is that rate: hashes per second.
Note the units aren't comparable across algorithms — 1 GH/s of Scrypt and 1 GH/s of SHA-256 are different work entirely, which is why Scrypt machines posting 'small' numbers earn comparably to Bitcoin machines posting huge ones.
Total network hashrate is Bitcoin's security budget: rewriting history would require out-hashing the entire honest network, and at hundreds of exahashes that attack is economically absurd — the physical fleet and gigawatts required exceed what any attacker could assemble quietly. Rising hashrate also signals miner conviction: it's capital committing to multi-year payback periods.
Your expected revenue is simply your hashrate over the network's, times the total reward stream. That fraction is also exactly how fractional mining shares work: Batch 1's machines produce 14 GH/s each on the Scrypt network, and each $100 share owns a pro-rata slice of the entire Batch 1 lot — about 58 MH/s of real, pool-verifiable hashrate working for you around the clock.