Definition - What does Block Size mean?
Block size in bitcoin refers to the size of a block of code representing a recent chain of bitcoin transactions. At a given point, a bitcoin block is added to other blocks to form a continuous chain, which facilitates the authentication of bitcoin transactions.
Techopedia explains Block Size
The current bitcoin block size is capped at 1 MB. To date, a flurry of new proposals, protocol rollouts, and debates have challenged the idea of keeping the block size at 1 MB, and floated the idea of upping the block size limit to 2 MB or above. A protocol called “Segregated Witness” or SegWit may eventually lead to block size increases. However, any block size increase would necessitate a “hard fork” or forced split in the bitcoin chain, which would break off a new cryptocurrency setup to be strictly delineated by its own participating community of users, miners and developers.