The Bitcoin halving is a programmed event that reduces the block reward by 50% approximately every 4 years (210,000 blocks). It's one of the most significant events in Bitcoin's monetary policy.
Halvings reduce new supply by 50%. With demand constant or growing, reduced supply issuance creates upward price pressure over time. All previous halvings preceded significant bull markets within 12-18 months.
The effect isn't immediate. Price doesn't pump on halving day. Historically, the major price appreciation occurs 6-18 months after the halving as the reduced supply gradually impacts the market.
Miners are most affected. Revenue drops 50% overnight while costs remain the same. Less efficient miners shut down, difficulty adjusts, and the network finds a new equilibrium.
Only 21 million BTC will ever exist. After all 32 halvings (around year 2140), no new Bitcoin will be created. Currently ~19.7 million BTC have been mined.