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.
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".
An open end 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.
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
A box wrench has that feature.
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.