Pokémon GO has introduced Link Charges, a new energy resource used to enter Mega Raids, including the more challenging Super Mega Raids. Trainers spend Link Charges to access these cooperative battles, allowing multiple players to tackle powered-up Mega Pokémon together. The system adds a layer of resource management, encouraging strategic planning of when and how to engage in high-level raids. By linking energy to raid participation, players can better pace their gameplay while taking on some of the toughest challenges in the game.
Source: Official Pokémon GO blog
Pokémon Blog 