Can I get a clear definition of "Pan-Pan", who and when may it be declared.

I have hard the USCG declare "Pan-Pan", followed by a requirement that all
none "Pan-Pan" traffic on channel 16 traffic be suspended.

Can an individual boat declare "Pan-Pan", say when a crew member is lost
overboard, etc??

I fairly sure I understand when I could send a "May Day" but, to me, Pan Pan
is something more recent and I must have missed out on earlier definition..

Thanks

Steve
s/v Good Intentions