The term dual ladder or double ladder is an ambiguous Go term that has been used to refer to anything that involves two ladders of either the same colour or different colours. These ladders occur simultaneously, but could be back-to-back in the case of a spiral ladder. There appears to be no consensus on the terminology for this set of techniques.
See the following pages for more information on the specific kinds of dual or double ladders. However, the page titles may not be the authoritative names for the respective techniques.