Coinbase

Coinbase is the special name given to the first transaction in every block. These can also be called 'Generation Transactions'. The winning miner creates this special transaction as part of the block templating process. A part of the coinbase is also used as an 'extra nonce' during the block discovery process due to a single ASIC miner being able to test more combinations than allowed for in the 2^32 possible combinations that changing the nonce in the block header can create.

The Coinbase transaction's outputs contain the block reward + the total of all transaction fees combined. The winning miner can pay this total amount out to up to 2^64 outputs.

While regular transactions refer to their parent transaction outputs to aggregate 'input' funds, a generation transaction has no parent.

The Coinbase transaction can contain any arbitrary data. The genesis block famously contains the dated title of an FT article:

The Times 03/Jan/2009 Chancellor on brink of second bailout for banks