The yellow collectibles in Rayman games are called Lums.
Lums are small pieces of magical energy found throughout the Rayman universe. In Rayman 2, collecting them helps reveal information about the world and its history, and gathering enough can open access to additional areas. They are both gameplay objectives and part of the series’ mythology.
Their colors can vary by game and function. In Rayman Origins, yellow Lums are the standard collectibles, while Red Lums are worth two yellow Lums. Some games also feature special colors with abilities or effects, so not every Lum should be assumed to be yellow or interchangeable.
Lums are easy to confuse with other Rayman collectibles, such as Electoons, Teensies, cages and Skull Coins. Those objects serve different purposes: Lums usually contribute to collection totals or power-related mechanics, while rescuing characters and breaking cages often advances exploration or unlocks rewards.