From Halopedia, the Halo wiki
List of seasons
Season points are a new in-game currency introduced with the Season system. They can be used within the various unlock tiers of each season to unlock armor permutations, skins, nameplates, Firefight voices, and more. Initially, season points could only be earned by progressing in the game's rank scheme through regular multiplayer, though the addition of Challenges has resulted in a wider array of season point earning potential across multiplayer, campaign, Firefight, Forge and custom games. Season points are a purely in-game currency, and cannot be bought through real-world purchases.