Larger case metal bracelet. Activity-specific features such as chronographs, altimeter, depth gauge.
I’d classify a fashion watch as something that can be used in a variety of casual situations, and combines form and function in a way that speaks to your personal style.
“Activity-specific” refers to the features that are built-in to a watch for a specific purpose. Diving watches are built to withstand underwater pressure, pilot watches typically have bigger numerals and dials so they’re easily read and adjusted at a glance.