A block in blockchain is a block of transactions. A block of transactions is processed on a regular basis with the interval dependent on the asset. Bitcoin for example processes a new block of transactions every 10 minutes. If there isnt enough room on the current block for a transaction, it will sit in a pool and wait for the next block in 10 minutes. Thanks to the lightning network, most bitcoin transactions can happen in seconds and then are settled on the chain later as the block is processed.
Block height is the number of blocks that have been created to date.