Sanyaku is the collective noun for the three ranks below yokozuna.
In reality though, ozeki is rarely included when the term is used, with the vast majority of incidences referring only to komusubi and sekiwake.
Unlike sumo's top two ranks, there is no special criteria for promotion to sanyaku. A simple winning record as the No. 1 or 2 maegashira is often all that is required.