What is the Bitcoin Halving (Halvening)?

For the first four years of Bitcoin's existence, the amount of new bitcoins issued every 10 minutes was 50. Every four years, this number is cut in half. The day the amount halves is called a "halving" or "halvening".

In the 2012 halving, the amount of new bitcoins (BTC) issued every 10 minutes dropped from 50 bitcoins to 25.
In 2016, it dropped from 25 BTC to 12.5 BTC.
In the most recent May 11, 2020 halving, the reward dropped from 12.5 to 6.25 BTC per block.
In the 2024 halving, the reward will drop from 6.25 BTC per block to 3.125 BTC.