In the context of the Nintendo Switch, an file is a "cartridge image" that contains the raw data from a physical game card. For Super Smash Bros. Ultimate

This report covers the technical and legal status of in the XCI file format for the Nintendo Switch. 1. Technical Overview of XCI Files

Downloading XCI files for games you do not own is considered copyright infringement. Most communities recommend "dumping" your own cartridge using a tool like nxdumptool to stay within a legal gray area.

, an XCI file allows the game to be played on a console with custom firmware or through certain emulators. Key Characteristics of SSBU XCI Files