Shoulder strap

A shoulder strap may be one of a number of things:

a length of fabric or other flexible material (such as leather, vinyl, rubber), used to suspend an item, often of some weight, from the shoulder(s). The strap may be worn slung over one shoulder or across the body. In the interest of comfort, they often have some manner of padding near the middle, where the strap rests directly against the shoulder or neck. Such items include purses, guitars, rifles, etc. In the case of rifles and other such weaponry, the shoulder strap is usually referred to as a sling. Shoulder straps may also be used in pairs on such items as a backpack or a baby carrier; the straps are worn one over each shoulder, and the item so carried is centred on the back or chest.
a length of fabric — usually one of a pair — used to support clothing, especially women's clothing, such as a dress, camisole, or brassiere. Shoulder straps such as these are usually made of the same material as the garment, and may be quite flimsy, as they are normally not expected to support much weight.

a length of fabric on a shirt, blouse, or jacket, running along the length of the shoulder; it is usually stitched into the shoulder seam and fastened with a button, snap fastener, or hook fastener near the collar. They are usually found on military or military-style civilian uniforms (such as park rangers or Boy Scouts), and are used to attach epaulettes, brassards, lanyards, slip-ons, or other insignia to the uniform.