Block halving is a manner of reducing the rate at which new cryptocurrencies are produced. It relates to the periodical halving situations that decrease the block awards given to miners.
Halvings are the core of the cryptocurrency models because they guarantee coins will be issued at a steady speed. This so-called halving is one of the main differences compared to traditional fiat currencies, which have an endless supply.
At the time of writing, November 2019, there have been 2 Bitcoin halvings. Which occurred in 2012 (28th of November) and 2016 (9th of July), the rate per Bitcoin at the first halving was $12, and during the second it was $650. As written in the code, the halving will take place after every 210.000 blocks. In total, there will be 64 Bitcoin halving events, when those all have occurred the maximum supply of 21 million Bitcoins is reached.
The halving is a fundamental function of the Bitcoin network and can be found on the Bitcoin Core Github.