The Bitcoin halving is a scheduled event that occurs every 210,000 blocks, approximately every 4 years, where the bitcoin with which miners are rewarded for inserting a block into the blockchain is halved.

Every time a new block is mined, new Bitcoins are issued as a reward to the miner who solves it. It is a key aspect of the Bitcoin protocol designed to control the issuance of new coins and keep the total supply of Bitcoin limited. Reducing miner rewards slows down the rate at which new coins are issued and limits the total BTC to 21 million.