No F9 key icon. Whats the use off this key?

I've a Dell Latitude 5420 laptop. I noticed that there are no icon on the F9 key. I searched on the google also. In dell website, there are a list where the F9 key is described as "Disable Camera" key. But, I can't find out any use of the key. Neither it disable camera or nothing function it can do. Can anyone tell me, what is the actual use of the F9 key?