A photographic material consisting of light sensitive silver salts, like silver bromide or silver nitrate suspended in a gelatin. The gelatin is normally supported by an inert, transparent base than can be glass or plastic or celluloid.
Light hitting the salt crystals forms a latent image, which is then developed by converting the silver salts to metallic silver.
After development, a fixing bath is used: this removes the residual silver salts (which would still be light sensitive).
This produces a negative image on the film.
In order to obtain a positive image, the negative must be reversed, usually by printing it.
There is still a large amount of black and white film being made and shot. Leading makers are Ilford, Kodak and Agfa. Black and white film is available in sensitivities going from 25 to 3200 ISO/ASA, and in more or less all film formats known to man, including a C41 process film in APS format.
Processing black and white film (and printing it) is relatively easy, and can be done at home on a modest budget (some hundreds of dollars).
It is also very educational for any budding photographer, and nearly mandatory for fine art photographers, because of the fine level of control that can be attained.