Block

• A grouping of transactions, marked with a timestamp, and a fingerprint of the previous block. The block header is hashed to produce a proof of work, thereby validating the transactions. Valid blocks are added to the main blockchain by network consensus.
• A block contains a set of data that holds all the information necessary to verify transaction and link the block back to its previous block in the chain.
• A block is a unit of the code the comprises the blockchain. It is the record of transactions that have occurred since the last block was created and a confirmation to previous transactions. Each block links to the block before it, thus creating a full block chain back to the original or “genesis” block.
• All blockchains have different block sizes. BTC currently has 1MB (2019), Dash 2 MB, BCH 32 Mb, Cypherium has an adaptable block size, etc.
• The following information comes from this post by Consensys (5-9-2019):

"The “block” in a blockchain refers to a block of transactions that has been broadcast to the network. The “chain” refers to a string of these blocks. When a new block of transactions is validated by the network, it is attached to the end of an existing chain. This chain of blocks is an ever-growing ledger of transactions that the network has validated. We call this single, agreed-upon history of transactions a blockchain. Only one block can exist at a given chain height. There are several ways to add new blocks to an existing chain. These are often termed “proofs,” i.e. Proof of Work (PoW), Proof of Stake (PoS), and Proof of Authority (PoA). All involve cryptographic algorithms with varying degrees of complexity.

Depending upon how a particular blockchain protocol was developed, the time that it takes for a block to be added to the canonical chain can vary widely. A blockchain is a linear construct in that every new block occurs at a later time than the one that preceded it and cannot be undone. A blockchain’s linearity serves as an ideal form of validation. According to ethstats.io as of July 2019, for the Ethereum blockchain, new blocks are added approximately every 14 seconds."