This is an advanced system of tone control in black and white pioneered by legendary landscape photographer Ansel Adams. The Zone System had and still has many fans, but is technically demanding and not always properly understood.
The scene is split into ten different brightness ‘zones’ from black to white, and the photographer plans the exposure to make sure all ten zones are recorded on the film. The next, crucial, stage, is the development process, where the contrast is adjusted to reproduce these zones in the print, though dodging and burning techniques may also be used on specific areas.
This second stage is impossible with film processed in rolls or cassettes, and the Zone System really only worked with sheet film cameras. It’s difficult to replicate with digital cameras because they don’t have the dynamic range of old-fashioned black and white film, which could record far greater extremes of brightness, a crucial factor in the effective use of the Zone System.