retention flip-flop
Beginner
A memory bit with a tiny backup, so it keeps its value while the rest of its zone sleeps.
Novice
A flip-flop (a one-bit storage cell) with a tiny backup cell powered by the always-on supply. It copies its value into the backup before the block powers off and copies it back on wake-up, so the block resumes where it stopped.
Expert
A shadow latch on an always-on supply with save and restore controls. It trades area and leakage for fast wake-up without software state restore; the save/restore sequence and the always-on supply routing to every retention cell must be verified.
Explained in Personal and edge devices (Industries).