A block in Bitcoin mining is a record of the most recent Bitcoin transactions that have not yet been recorded in any prior blocks. Once a block is completed, it is added to the blockchain and becomes part of the permanent, public record of all prior Bitcoin transactions.
The completion of a block is verified by Bitcoin miners and, once verified, the block is added to the blockchain.
The process of creating and verifying blocks is called mining. Miners are rewarded with newly minted Bitcoins for their work in verifying blocks.
In addition to being rewarded with new Bitcoins, miners are also compensated with transaction fees paid by users for including their transactions in a block.
The first transaction in a block is called the coinbase transaction and is used to pay the miner who verified the block. The coinbase transaction includes a special field that contains an arbitrary number of bytes.
In order for a block to be valid, the coinbase transaction must be the first transaction in the block and must be valid according to the Bitcoin consensus rules.
The Bitcoin network difficulty adjusts every 2016 blocks to ensure that on average new blocks are created every 10 minutes. The difficulty adjustment mechanism ensures that as more miners join the network and attempt to mine blocks, the difficulty of creating new blocks increases, thus keeping the average time between new blocks at 10 minutes.
In summary, a block in Bitcoin mining is a record of recent Bitcoin transactions that have not yet been recorded in any prior blocks. The process of creating and verifying these blocks is called mining, and miners are rewarded with newly minted Bitcoins and transaction fees for their work.
The first transaction in each block is called the coinbase transaction and is used to pay miners for their work in verifying the block.