What is halving and how it's bullish for Bitcoin?

I'll tell you in a straight way.

BTC halving means the mining reward for bitcoin miners will cut in half. The reward will drop to 3.125 bitcoin from the current 6.25 bitcoin.

Bitcoin is the most demanded crypto currency right now. As the mining reward will reduce it will slow down the new BTC supply.

Now you need to know a basic economic rule.

High demand + Less supply = High prices.

As demand continues to increase and there will be less supply in the market it will result in the higher prices.

That's it .