IP Filter Documentation.

The FAQ at OpenSUSE is a fine document.  On the page 
www.openbsd.org/faq/pf/tables.html I found this "or the self keyword".  On the 
page www.openbsd.org/faq/pf/filter.html I found this "table <firewall> const { 
self }".  And finally, I think, at www.openbsd.org/faq/pf/nat.html there's this 
"The word self will appear if the state is floating".  All of which are nice. 
What exactly is "self"?  The computer has two NICs, which one is "self"?  Is it 
context dependent?  Along that same line, where can I find a list, with a 
definition, of "keywords" for IP Filter?  They're mentioned a lot.

Any and all help would be appreciated.