The term hash rate refers to the speed at which a computer is able to perform hashing computations. In the context of Bitcoin and cryptocurrencies, the hash rate represents the efficiency and performance of a mining machine. It defines how fast a mining hardware operates when trying to compute a valid block hash.
In short, the process of mining involves a myriad of hashing attempts, until a valid hash is produced. In other words, a Bitcoin miner needs to run a bunch of data through a hash function in order to produce a hash, and they are only successful when a certain hash value is generated (a hash that starts of a certain number of zeros).
Therefore, the hash rate is directly proportional to the profitability of a miner or mining pool. A higher hash rate means that the probability of mining a block is higher and, thus, the miner has a better chance of receiving the block reward.
Typically, the hash rate is measured in hashes per second (h/s) along with an SI prefix, such as mega, giga, or tera. For instance, a blockchain network that computes one trillion hashes per second would have a hash rate of 1 Th/s.
The hash rate of Bitcoin reached 1 Th/s in 2011, and 1,000 Th/s in 2013. In the early stages of the network, users could mine new blocks using their personal computers and graphics cards. But with the creation of specialized mining hardware (known as ASIC miners), the hash rate started to increase very fast, causing the mining difficulty to rise. Thus, personal computers and graphics cards are no longer suitable for Bitcoin mining. Bitcoin’s hash rate surpassed 1,000,000 Th/s in 2016, and 10,000,000 Th/s in 2017. As of July 2019, the network is operating with roughly 67,500,000 Th/s.