This article is from the Recreational Figure Skating FAQ, by Karen Bryden with numerous contributions by others.
A mohawk is either open or closed, depending on the position of the
free skate just before the turn. For an open mohawk, the heel of the
free foot is placed on the ice at the inner side of the skating foot.
For a closed mohawk, the free foot is placed on the ice behind the
heel of the skating foot.
Although people with closed hips often have an easier time with the
closed (i.e. step-behind) mohawks than with the open ones (i.e. free
foot at instep), the terms "open" and "close" have nothing to do with
the position of the hips before or after the turn. Originally, the
terms related to the trace on the ice: On a mohawk done with the feet
close together close to 90 degrees the traces left by the starting and
the finishing foot cross in an "x" shaped, i.e., the arc described by
the skater is "closed". On a change of feet with feet apart turned out
close to 180 degrees the traces do not cross and the arc is "open".
This turn was known as an open mohawk. Later on, the name mohawk
became applied only to the kind where the traces cross (the formerly
open mohawk is nowadays usually referred to as a "step from forwards
to backwards" or "step from backwards to forwards") and the terms
"open" and "close" adquired their current meaning given above.
There are other variations of the basic mohawks, used mainly in the
context of ice dancing. They are often based on the position of the
free leg after the turn. These variations are often named after a
dance where they are executed (for example, the "Fiesta tango mohawk"
or the "Foxtrot mohawk").