[Q]: Interpretation of my .forward file?

I have procmail running now after some struggle. I could't get .forward to
work with the suggested lines so I stole and edited the line from another
user on my system. This works, but what does it mean? I'm not sure if it
is appropriate to my usage. I'm unclear about -f- and -d, exit 75, and why
my username is called twice. Actually, I don't understand any of it!

|IFS=' '&&exec /usr/local/bin/procmail -f- -d dnhunt||exit 75 #dnhunt

David <dnhunt(_at_)rain(_dot_)org>, using procmail v3.11pre3