The Maximum Aperture
The limit to how wide your lens aperture blades can open is its maximum aperture.
Different lenses have different maximum apertures. They are not all the same! The maximum aperture is part of the lens name...
A 50mm f/2.8 lens - has a maximum aperture of f/2.8
A 200mm f/4 lens - has a maximum aperture of f/4.0
Photographers can make use of maximum aperture when they are trying to blur the background and isolate the subject. If they are shooting in a low light situation (indoors or night), they could open the aperture wide and get a brighter image.
The Minimum Aperture
The minimum aperture is how closed up the blades can get. Most lenses have no issue with this and can close to f/16 or even f/22. A photographer could use a minimum aperture on a very bright day or when they are trying to get as much of their scene in focus as they can.