A Block header is like the metadata of a Bitcoinblock - it's a summary of all the key information about that block, like a title page or a table of contents. It includes things like the version number, the previous blockhash, the timestamp, and the nonce.
Example
"Miners have to create a valid block header before they can add a new block to the blockchain, it's like the key that unlocks the next page in the ledger."
"Block headers are used to verify the integrity of the blockchain, by checking that each block is correctly linked to the previous one in the chain."
