# df -h
Filesystem      Size    Used   Avail Capacity  Mounted on
/dev/ada0s1a    918M    552M    292M    65%    /
devfs           1.0K    1.0K      0B   100%    /dev
tmpfs           5.0M    2.9M    2.1M    57%    /etc
tmpfs           5.0M    2.2M    2.8M    45%    /var

# mount
/dev/ada0s1a on / (ufs, local, read-only)
devfs on /dev (devfs, local)
tmpfs on /etc (tmpfs, local)
tmpfs on /var (tmpfs, local)

/cfg is not normally mounted and holds /etc files you want to override.
/dev/ad0s2a is a slice to hold a backup system image you can boot if
something went wrong with your primary slice.  Normally it is not
mounted too.