Flat sheet
Microfiche is not rolled like microfilm. The sheet format is one of its defining features.
Microfiche definition
Microfiche is a flat sheet of transparent film that stores miniature images of documents.
That is the core definition. A single microfiche sheet can contain many reduced page images arranged in a grid, which makes it useful for archival storage, library preservation, and access to large paper collections in a compact format. Because the images are reduced so heavily, the sheet normally needs a special reader for comfortable viewing.
Expanded definition
Microfiche is a type of microform. Instead of storing information as full-sized paper pages, it preserves photographic reductions of those pages on a flat transparent sheet. Institutions use it when they need compact storage, preservation copies, or access to materials that were archived before digital systems became standard.
Key parts of the definition
Miniature images
The content is reduced photographically, which is why one sheet can hold many pages.
Archival use
The format is associated with preservation, reference collections, and historical records access.