Field-of-view is the angular extent shown through the lens. For fixed-lens cameras, and all web-cams that I know of, the field-of-view is normally stated relative to sensor-size. This is very reasonable since the lens is fixed and cannot server on something else.

While this sounds like numbers could be compared, there several reasons why not:

• Field-of-view can be measured vertically, horizontally and diagonally. Those numbers are not the same but some manufacturer only quote one of them and do not say which one. If you have to guess, it is usually the diagonal field-of-view.
• Field-of-view changes with focus. As a lens focuses, there is often change in its field-of-view, particularly when close-focusing. Most field-of-view numbers are stated with the lens focused at infinity. Actually, even the focal-length changes when away from infinity! Unfortunately, there is no formula for what happens to field-of-view as focus is changed because it depends on the particular optical design of the lens.
• Field-view varies with aspect-ratio. On cameras that shoot with different aspect-ratio, a reduced field-of-field is possibly shown. Only a few makers special field-of-view by aspect-ratio. A common example is switching between SD (4:3) and HD (16:9) video but the same thing applies with image-formats (3:2, 4:3, 1:1, etc).
• Digital processing reduces aspect-ratio. Certain features reduce the displayed aspect-ratio to save some boundary pixels used in their computation. This is always the case for electronic stabilization and most often used for multi-shot techniques like Multi-Frame Noise-Reduction, and HDR plus geometric corrections such as distortion correction,