What is the difference between a Boeing Line number and a Block number?
Here is Boeing's Examples 

Block numbers 


ZA001 Onwards - B787-8
ZB001 Onwards - B787-9
ZC001 Onwards - B787-10
ZD001 Onwards - rebuild of prototypes
ZE001 Onwards - B787-9 with customizations


Line numbers are the serial number of the aircraft of that aircraft type

Serial Number is the manufacturers serial (basically the number of aircraft they have built up to that aircraft)

Airbus doesn't use the Boeing Line/Serial numbers, they use a different system where the aircraft serial number is in fact the aircraft line number and the total # of the aircraft being built.