A Subduction

1. The action of being pushed or drawn beneath another object.
2. (geology) The process of one tectonic plate moving beneath another and sinking into the mantle at a convergent plate boundary.Subduction - Wikipedia
3. The act of subducting or taking away.
4. Arithmetical subtraction.
5. (mathematics, mathematical analysis) A surjection between diffeological spaces such that the target is identified as the pushforward of the source.