expansion pack

Noun

 * 1)  A module that adds new content to an existing piece of software.
 * 2)  An add-on for a video game that includes additional content and is typically sold separately.

Usage notes

 * An expansion pack is generally understood to include a substantial amount of content, even comparable to the base game itself, whereas the more general term DLC is usually size-agnostic and refers to content distributed as a download.