What defines a side-winder watch?

A side-winder watch is specifically defined by the location of its winding stem, which is situated at the 3 o'clock or 9 o'clock position on the case. This unique positioning provides both functional and aesthetic advantages, particularly in enhancing the watch's design and ease of use. For example, having the winding stem on the side allows for a more ergonomic grip and can improve the overall user experience when adjusting the time or date settings.

The other characteristics listed in that question, such as a digital display, waterproof capabilities, or features addressing multiple time zones, do not inherently define a side-winder watch. Each of these aspects may pertain to different types of watches but do not relate to the defining feature of a side-winder. Thus, the defining characteristic of the winding stem's placement is what accurately identifies this specific category of watch.