Parts of a sail

In sailing the parts of a sail have certain terms that clearly describe them.
There are two types of common mainsails. The Three Sided Mainsail and the Four sided Mainsail. Each of these Mainsail types have many different names according to exact location and relationship of supporting spars.
Parts of a headsail.
The headsail of a sailboat is any sail set forward of the mast (on a single masted boat) or foremast (the mast nearest the bow). The corresponding parts are the same relative to the front of the boat. (Note: The headsail tack is the name for the lower corner of the headsail -- the sail closest to the front of the boat.)