"Unlockable items" refers to special things or rewards that can be obtained by completing certain tasks or achieving specific goals in a game or other activity. Full definition
There is a wealth of unlockable items for each character class, but Konami's post-launch support for MGO has primarily consisted of paid cosmetic upgrades. (polygon.com)
Both of these are optional challenges, but will yield extra unlockable items for skilled players. (theplatformer.net)
What Needs Improvement: Merida's animated hair quality does not equal the film, dodge as unlockable item instead of a basic action (geardiary.com)