There is a specific development process for each type of film.
For example, slide films are developed in the E6 process and color negative films in C-41.
Cross development, cross processing, X-Pro, or cross processing refers to developing a film in the wrong process.
For example, a slide film can be developed in the C-41 process for color negative films.
You get different effects depending on the film you use.
Usually the images are very high in contrast.
Often there are color shifts, so some slide films deliver really green or pink images.
Some, on the other hand, do not produce color shifts, but only higher saturation of colors and strong contrasts.
Grainy images can also result from cross processing in C-41.
Photo: Markus Winkler | Example photo of a cross processed DM Paradies Dia 100
Sensia 100 crosseted in C-41