In the Dance Central series, songs can be played on multiple games through importing. An import is when an object is taken from one source and put onto another. In the case of Dance Central, songs are the objects that can be imported.
Importing has since been disabled. Players who have not imported do not have the option to anymore. But if players have previously imported songs, they can still access them in the game.
An import can comes in one of two ways: through a code or done automatically. For songs that originate from Dance Central or Dance Central 2, they can be imported into another game by using a code. The code is given in the manuals of the games, which the player can hold onto until they are ready to use it.
Songs from Dance Central can be imported into either Dance Central 2 or Dance Central 3 while songs from Dance Central 2 can only be imported into Dance Central 3. (Songs from Dance Central 3 cannot be imported into any other game, and on-disc songs from any game cannot be imported into Dance Central Spotlight) Once a player imports songs from one game to another, they do not have to import it again onto a third game, although this case only happens with songs from Dance Central. Due to this, players will not be able to play songs from Dance Central 2 on Dance Central, and they can only play them on Dance Central 2 or Dance Central 3. Note that songs only come in two imports: one that includes all of the songs from Dance Central and the other, all of the songs from Dance Central 2; they cannot be individually imported.
The second method is done automatically. When a player purchases a downloadable content song (either alone or in a pack), the content will appear on the game they purchased it from, and on any games they're applicable to, including Dance Central Spotlight. Depending on when the content was first released determines what games the song can be played on. (i.e. if a song was released as downloadable content on Dance Central 2 first, the song can also be played on Dance Central 3 and Dance Central Spotlight, but it won't be able to be played on Dance Central)