A shirt that has no shoulder straps, attached sleeves, halterneck or other shoulder- or collarbone-related attire holding up the upper portion of the shirt, instead relying on the tightness of the shirt's neckline to keep it in place. The shoulders and upper chest area should be bare.
A strapless shirt is similar to a tube top, but is not completely the same as one; the difference between a strapless shirt and a tube top is that:
A tube top is tight-fitting from top to bottom. As the name indicates, a tube top is generally tube-shaped.
A strapless shirt can be loose fitting at the bottom, and may extend past the waist. Strapless shirts can also have pronounced bust cups, which are usually not present in tube tops. As such, the strapless shirt tag can be useful to describe any strapless upper-body garments (excluding dresses) that don't exactly qualify as a tube top.
For the shirt to qualify as a strapless shirt, the shirt must not have attached sleeves or held up by straps. If sleeves are attached, then the shirt is an off-shoulder shirt. If it is held up by straps, then it is a camisole.
