What is a Block?
A block in cryptocurrencies refers to the collection of transaction data, and it is the basis of the blockchain protocol.
Each transaction creates a set of data, and this data is gathered together until it is as large as the definition of a block for the given blockchain.
Once the block is created it is queued to be processed for verification of the transactions contained within the block.
This process of transaction verification is known as mining, and it is another of the fundamental basics of blockchains which operate under a proof of work consensus model.