Bitcoin mining means validation of a block and finding a solution to a complex puzzle to help run the bitcoin network, miners are paid to maintain the network status. As a matter of fact , a new block is mined and added to the chain in every 10 mins.
For every succussful mining of a block, the miner is given a monetary award in the form of newly created bitcoins.(which is 12.5 btc now ). The reward amount reduces to half after every 4 years or 210,000 blocks, the event is known as halving.
The code dictates that 21 million coins will be released over the course of bitcoin's lifecycle. This means that once there have been 64 halvings, there should be no further nSubsidy released. In other words, after 50 has been divided 64 times, the last bitcoin will have been released into the market and the total 21 million supply will be in circulation.
Miners, as one can imagine, stand to be impacted the most when the next halving event takes place. Actually, the block reward for miner is made up of newly created btc and the transaction fees attached to each transaction validated by the miner. Now, once the btc count will rerach to 21 million then the creation of new btc will stop and the miner will soley be rewarded with the transaction fees.
