What do the "shiwat" and "rhiwat" columns mean in output of netstat -v?

Question

The output of netstat -v includes the following column labels:

Proto  Recv-Q  Send-Q  Local Address  Foreign Address  (state)  rhiwat  shiwat  pid  epid  state  options

man netstat does not explain the meaning of the "rhiwat" and "shiwat" columns, and I have also been unable to find an explanation in search engines or here/on stackoverflow.

What do the numbers in these columns mean?

Answer 1

I looked at the BSD netstat man page and I see the following:

R-HIWA    Receive buffer high water mark, in bytes.
S-HIWA    Send buffer high  water mark, in bytes.