Bitcoin halving is a pre-programmed event that occurs approximately every four years, in which the number of new Bitcoins generated per block is cut in half. This process is built into the Bitcoin protocol and is designed to limit the supply of Bitcoin in circulation and control inflation. 

When Bitcoin was first created in 2009, the reward for each block mined was 50 Bitcoins. In 2012, the first Bitcoin halving took place, reducing the reward to 25 Bitcoins per block. The second halving occurred in 2016, reducing the reward to 12.5 Bitcoins per block. The most recent halving took place in 2020, reducing the reward to 6.25 Bitcoins per block.

The halving process is significant because it reduces the rate at which new Bitcoins are created, making it more difficult and expensive for miners to earn rewards. This can have an impact on the overall supply and demand of Bitcoin, potentially leading to an increase in its value. However, it is important to note that Bitcoin's value is determined by many factors, including market demand and adoption, and not solely by the halving process.