n.1. The act of superposing or the state of being superposed: "Yet another technique in the forensic specialist's repertoire is photo superposition" (Patrick Nuyghe).
2. Geology The principle that in a group of stratified sedimentary rocks the lowest were the earliest to be deposited.
3. Physics The combination of two or more physical states, such as waves, to form a new physical state in accordance with the superposition principle.