I am not sure what you mean ?
If you are referring to a label on the film that says you can get up to 16 frames ... this would be the maximum depending on the camera format:
A 6x6 camera will use 12/13 frames on a 120 film.
A 6x4.5 camera will use 15/16 and a 6x7 camera will use 10.
i have a 12 frame back and when i went to get film i wasent specific and asked if it was 12 frames. and when i went to go put one roll in i fudged it up and looked at it and it was 16 frames. can 120 film that has 16 frames on it work in a hasselblad film back thats meant for 12 frame 120 film?
The 'number of frames' on a roll of 120 film [or any film, for that matter] depends entirely on the camera in which it is used.
If 120 film is used in a camera which produces 6cm x 6cm 'frames' or images, you will get a total of 12. If the camera produces 4.5cm x 6cm images, you will get 16 images. There are still further possibilities. 6cm x 9cm will get you 8 images/roll.
There are 'half-frame' cameras which use 35mm film. A cassette of film which will produce 36 images in a standard 35mm camera [Contax, Nikon, Minolta, etc.] will produce 72 images in a half-frame camera such as an Olympus Pen or a Mercury.
Like was explained, it depends on the size of exposure that the camera makes. If you think about a roll of film, there's not specific spots that will expose and won't. It's one constant roll of film that can be shot/exposed anywhere on it. Maybe that will help you visualize what people are saying.