lun

hi,
I like to see your opinion on below.What is lun?

A logical unit number (LUN) is a number used for identifying a logical unit relating to computer storage.
Any LUN created smaller than 6 GB will be allowed to grow to 64 GB due to its geometry, referring back to the 1 MB cylinder size with 65535 cylinders. How a number has some size(here 6gb)?
A logical unit number (LUN) is a unique identifier for designating an individual or collection of physical or virtual storage devices.
A uniq identifier?a number?
A LUN is a logical volume from the point of view of the storage.
What is LUN ID?-id of a number?
https://whatisanything.com/how-do-i-get-the-wwid-of-a-lun-in-linux/