Subduction is from the Latin, “sub” meaning “under” and “ducere”, “to pull”. It is a limit between plates where the lithospheric plates are converging, i.e. approaching each other, with one plate (generally oceanic) sliding under the other plate (oceanic or continental).
This happens at the convergence of plates (oceanic or continental). Along the line of convergence, the denser plate passes under the other one. This is called subduction.