A block halving is a process of reducing the rate at which new cryptocurrency units are generated. Specifically, it refers to the periodical halving events that decrease the block rewards provided to miners.
Halvings are at the core of the cryptocurrency economic models because they ensure coins will be issued at a steady pace, following a predictable decaying rate. Such a controlled rate of monetary inflation is one of the main differences between cryptocurrencies and traditional fiat currencies, which essentially have an infinite supply.
Halvings reduce the emission rate of DFL per day and make it more scarce. The cycle is every 30 days where the amount of DFL minted per day is cut in half. This action only impacts the main Farms that source funds from newly-minted DFL. Mini Farms and castles won't be affected because rewards for these pools are sourced elsewhere (from Defily team budget, DAO budget, third party partner budgets, etc.)