The term cell library refers to a component of a DGN library that contains cells — usually one per model. Recall that cells are small drawings — usually of frequently-used or complex symbols.

Cell libraries used with previous versions of MicroStation are standalone files in a special format that is not directly supported by MicroStation. Pre-V8 cell libraries are automatically converted to DGN libraries when attached to a DGN file in MicroStation, but they retain their extension, typically ".cel."