It's more bullet weight (than actual bullet) and approximate velocity.

If you do some digging on the specific scope, you'll likely find info on the subtentions.

Here's a Leupold chart for some of their ballistics aiming systems:

https://cdnp.leupold.com/products/p...g-system-manual.pdf?mtime=20170626163401

[Linked Image from i.imgur.com]

WWP53D