Coinbase reward is the name of the coins that a miner receives when he finds a block.

First they where 50, then 25, then 12.5 and now 6.25 ₿ per block.

The trick is: these ₿ are “locked” till some time after finding the block. This is for a simple reason: sometimes competing blocks are found and briefly coexist before the weakest chain (with least POW behind it) reorganizes and starts to build on the strongest chain again. This is called a reorg.