What is a coinbase reward and how is it different from a fee?

The coinbase reward, sometimes called the block subsidy, is the newly created MLRT paid to whoever mines a block. It is brand-new coins entering circulation, defined by the emission schedule. Transaction fees are different: they are existing MLRT that senders attach to their transactions to have them included, and they go to the miner on top of the coinbase reward. Today the coinbase reward is the larger part of miner income; over time, as emission slows through halvings, fees grow as a share. Together they make up your total block revenue. The word coinbase here refers to the special first transaction in a block, not any exchange or company of the same name.