Reversal film produces a positive image on a transparent base. The film is processed to produce transparencies. This means that what you see on camera is the resulting image.
They are then made into a slide, the most common of which is 35 mm slide, with the image framed in a 2×2" cardboard or plastic mount.
These films are the preferred film choice of professional photographers for images intended for reproduction in print media. This is because of the films' high contrast and high image resolution compared to negative (print) films.
You can get a wider range of tones and colours on a slide than a print, just as an image on a monitor will be more vibrant than any print.
We did a range of colour transparencies on a medium format camera in class.