The number of cryptographic hashes per second (H/s) a computer executes for blockchain mining such as Bitcoin.  A hash rate may refer to computations in a single GPU in one computer, a crypto mining machine, or hundreds of machines in a mining datacenter (see 
ASIC miner).  See 
cryptographic hash function.
Quintillions of Hashes per Second
For example, CleanSpark is a top North American public Bitcoin miner.  In January 2022, its total hash rate exceeded 2 EH/s (two quintillion hashes per second).  In that year, the company was rewarded with an average of 10 bitcoins per day, which means all the machines combined solved a mathematical puzzle 10 times (see 
Bitcoin halving).  The idea is that if hard work is done, even if just numbers being calculated in a computer, there should be a reward.  Bitcoin's Satoshi Nakamoto employed that concept (see 
Satoshi Nakamoto).  See 
space/time.
A CleanSpark Datacenter
After expanding with more machines, by 2025, CleanSpark reached 40 EH/s.  (Image courtesy of CleanSpark.)
 Hashes Per Second
 KH/s  Khash/s  Kilo (thousand)
 MH/s  Mhash/s  Mega (million)
 GH/s  Ghash/s  Giga (billion)
 TH/s  Thash/s  Tera (trillion)
 PH/s  Phash/s  Peta (quadrillion)
 EH/s  Ehash/s  Exa  (quintillion)