It's used for turning nuts or bolts. The open end makes it easier to use.
Open end wrench, box wrench, gear wrench.
There is no Allen wrench, I believe it is 14 mm open wrench.
An open end wrench.
If you are referring to the type of wrench that usually has an open end to tighten the bolt or nut and a point on the other end...the point is called a "drift pin" and is used to line up the hole that the bolt is going into. That style of wrench is called a "drift pin wrench".
A box end wrench is used to undo or tighten nuts when a lot of torque is required. When working under my car on exposed nuts and bolts, a box wrench will remove nuts that an open end wrench will 'round'.
A combination wrench has an open end on one end and a box end on the other. The 18mm designates what size nut/bolt the wrench fits.
Adjustable Wrench , open end wrench , box wrench, socket wrench, monkey wrench
An open ended wrench with 2 sizes -ie 1/2 and 9/16.
A box wrench has that feature.
Open end, box end, with 6-point or 12 point box end, flare end, ratcheting end-wrench, Crescent (or aka adjustable), crowsfoot, pipe wrench and more
With a boxed end wrench or socket, never with an open end wrench.
An open end wrench is ideal for loosening or tightening bolts or nuts especially if they are located in a particularly hard to reach area. Open end wrenches can be purchased at hardware stores like Home Depot.