About "Number of AU's Assigned to This Aggregate" section in Storage-pool-aggr.xml's Autosupport

Hello people

quick question about section "Storage-pool-aggr.xml" of any Autosupport.

There is a label/field/column "Number of AU's Assigned to This Aggregate" with a number for each aggregate non-root.

What is exactly the meaning of that number specifically?  what does it represent?

thanks n Rgds