Is there a unit for F value? What do you mean when you see some shots saying f=60mm? F=60mm corresponds to the F value set by the SLR.

F is the abbreviation of focal length, which is focal length. The focal length is the length. Of course, there are units. F=60mm means the focal length is 60mm.

Aperture is also a length, but for convenience, the size of aperture is usually expressed by focal length ratio, that is, the ratio of focal length to aperture, such as f/2.8, f/5.6, etc. (f is the focal length,/is the division symbol). Some photographic equipment manufacturers use capital F to represent the focal ratio, which is called "F value" or "aperture value" in China, such as F2.8 and F5.6, and this value marked on the lens indicates the maximum aperture that the equipment can reach.

So f=60mm refers to the focal length, and the f value set by the fuselage indicates the aperture.