what is meaning in zfs list - REFER column?

Hi all,

I checked the doc Managing ZFS File Systems in Oracle® Solaris 11.4 P.118

"referenced Number N/A Read-only property that identifies the amount of data accessible by a dataset, which might or might not be shared with other datasets in the pool."

is the REFER column same as USED? What is the meaning of REFER? I am a bit confused.

and df -h seems to review the pools available size and not the storage actual size?

Is the pool supposed to be compressed? how come df -h have the same values as zpool list?

# zfs list

NAME                   USED AVAIL REFER MOUNTPOINT