A CBZ file is a digital comic book archive file format, similar to a ZIP file, but specifically designed for storing and distributing digital comics, including manga. It contains a collection of images, usually in JPEG or PNG format, that are compressed and stored together in a single file.
A guide on manga CBZ files!
Not all apps support the specialized features manga needs, such as reading or automatic cropping. Manga Viewer - CBZ(CBR) Reader - App Store manga cbz files