Halving is a programmed event in a cryptocurrency's protocol that occurs at predetermined intervals, typically every few years. During a halving event, the mining reward for validating new transactions on the blockchain is reduced by 50%, which effectively slows down the rate at which new coins are created and controls the currency's overall supply.
The purpose of halving is to ensure the scarcity and value of the cryptocurrency over time, as well as to incentivize miners to continue supporting the network through transaction validation. Halving events are closely watched by investors and traders, as they can have a significant impact on the price and supply of a given cryptocurrency.