"Soul gems" refers to magical stones or crystals that contain the essence of a person's soul. They are often used in fantasy games, movies, or stories to store or manipulate souls, either for power or resurrection purposes. Full definition
The comics» origins see the Infinity Stones introduced as Soul Gems before Thanos labels them «Infinity Gems», which has stuck ever since. (gamesradar.com)
For instance, collectible upgrades called soul gems unlock the most powerful skill for each character. (quartertothree.com)
Finding Soul Gems allows you to buy the respective Skylander's ultimate ability and be treated to a short cinematic showing off the character's moves (inspiring you to buy the ones you're missing). (gamesradar.com)