"Moby Dick" is the name of a
Led Zeppelin instrumental song on the album
Led Zeppelin II, which is largely a
drum solo showcasing
John Bonham. In concert, Bonham would extend his solo until this song reached a half-hour in length. The live version on
The Song Remains the Same soundtrack is not quite that long, just under 13 minutes.
According to the site cited below, "Moby Dick" grew out of a piece called "Pat's Delight" played when Led Zeppelin first came together, and also had roots in "The Girl I Love (She Got Long Black Wavy Hair)," which can be heard on the BBC Sessions album. It went in and out of the set list until finally retired after the 1977 tour.
Source:
http://tinpan.fortunecity.com/leonard/849/songs/mobydick.html