Blanket clemency is clemency granted to multiple persons and can be in the form of a pardon, shortening of a prison sentence, or a commutation of a sentence, or a reprieve. Most states' governors and the President of the United States have the power to grant clemency; In other states, that power is committed to an appointed agency or board, or to a board and the governor in some hybrid arrangement.
You do not necessarily need to be convicted to receive a pardon. Depending on the exact formulation of a blanket pardon, and the specific underlying legal framework of course, the pardon can even protect from future prosecution. In the United States specifically, preemptive Presidential pardons have been issued.
Examples President Jimmy Carter pardoned men who evaded the Vietnam War draft, fulfilling a controversial campaign promise. President Donald Trump's pardon of January 6 United States Capitol attack defendants. Retiring Governor George Ryan of Illinois issued a blanket clemency to all death row inmates after special clemency hearings in January 2003.
References
-PJStar.com Katy Chevigny and Kirsten Johnson, Deadline, Big Mouth Productions, 2004.