A lens usually has three rings.
1 - focus ring
2 - aperture ring (might be absent on modern lenses)
3 - zoom ring (might be absent if the lens is only single focal length (prime/fixed)
For prime lenses, one would 'zoom' with their feet
For instance, a lens could be a zoom, say 18-50mm. But a prime/fixed lens would be something like 50mm only.
While not always true, a prime/fixed lens needs less glass in the lens than a zoom lens. This makes it 'easier' to create sharper lenses with wider apertures.
Also, while not always true, zooms commonly have variable widest apertures to reflect the zoom length.
For reference, you can see in my signature that I have 3 zooms and 5 primes.