Borough, Block and Lot

Borough, Block, and Lot (also called Borough/Block/Lot or BBL) is the parcel number system used to identify each unit of real estate in New York City for numerous city purposes. It consists of three numbers, separated by slashes: the borough, which is 1 digit; the block number, which is up to 5 digits; and the lot number, which is up to 4 digits. 
The borough number is:
An example of a valid style of BBL is 4/99999/9999 for Queens.