Downloadable content
From VNDev Wiki
Downloadable content, or DLC, is any game-related content that can be downloaded by the player after the purchase of the original game. DLC may be available for free or require purchase, but the term used alone often indicates paid content, with unpaid content being marketed as “free DLC”. DLC may also be called expansions or add-ons.
Common forms of DLC content for visual novels include: soundtracks, digital artbooks, or extra stories/routes (which are sometimes offered on fandiscs). DLC which adds new story content is similar to a content patch.
For something to be considered DLC, it must have been released (or authorized) by the official creator of the original game. Unofficial, fan-created content might include mods and fanart.