Bitcoin Halving is an event where the number of Bitcoin rewards generated per block is halved (divided by 2). The total amount of Bitcoin mined by miners per block will decrease from 12.5 to 6.25 BTC in the next half of Bitcoin. This means that after the event, Bitcoin miners will be rewarded with 6.25 BTC, which makes the supply of BTC less and less.

When Satoshi Nakamoto created bitcoin, he wanted to create a system that would maintain itself and in some way simulate gold mining. Over time, mining will become more difficult and rewards will gradually decrease to control the supply.