The hash rate is a way to measure how much processing power there is backing the Bitcoin network.
Hashes are key to securing transactions on the Bitcoin blockchain and as more ASICs come online to compete for block rewards, Bitcoin’s protocol will adjust the hash rate to make mining more difficult.
By doing this, the network becomes even more secure and even more difficult to attack.
An attack on the Bitcoin network would come in the form of a single entity being able to control over 51% of the hash rate, which gets more costly due to the capital expenditure required to buy ASICs, set up infrastructure and maintain their miners.
By the time the attacker would have control of the hash rate, those smart cookies already on the network will know about it and it becomes a very costly exercise for the attacker if it doesn’t work.