The block subsidy is the newly issued portion of a miner’s block reward. It began at 50 BTC and is cut in half every 210,000 blocks. It is separate from transaction fees.
A miner may claim less than the permitted subsidy, but not more. Every full node calculates the allowed amount and rejects a block whose coinbase output overclaims the subsidy plus fees.
Repeated integer halvings drive new issuance toward zero. The schedule bootstraps security while distributing coins, then progressively shifts miner revenue toward transaction fees.
For the clearest picture, read this entry together with Halving, 21 Million, Mining, Transaction Fees, Genesis Block. The reverse links also lead from Genesis Block, Proof of Work, Mining, Difficulty Adjustment.
New issuance, not total miner revenue
Halves every 210,000 blocks
Nodes reject overpayment
Trends toward zero