.cia files are used to distribute and install games, demos, and other applications on the Nintendo 3DS console. They are essentially containers that hold the necessary data for the console to install and run a particular title.

, allowing games and apps to be installed directly to the console's NAND or SD card so they appear as permanent, launchable icons on the home screen. Hacks Guide Wiki Key Features of .cia Files Direct Installation

Additionally, the ( title.db and import.db ) will contain entries with 0x00000000 for the ticket signature type.