Credits are a form of in-game currency in every game since Modern Combat 3: Fallen Nation.
Modern Combat 3: Fallen Nation Edit
Credits are seperated into local play (blue credits) and online play (yellow credits). Blue credits can be used to upgrade weapons or items in he campaign (permanently) or to unlock things in local multiplayer.
Modern Combat 4: Zero Hour Edit
Modern Combat 5: Blackout Edit
In Modern Combat 5: Blackout, credits can be purchased in fixed amounts with real-world currency, as well as acquired by completing campaign missions, multiplayer matches, and Activities. Credits can be used to purchase Supply Packs, Power User status, as well as blueprints in the Black Market.