The volume displaced by a single stroke of a piston in an engine or pump.
From Merrian-Webster: Main Entry: dis·place·ment Pronunciation: di-'splA-sm&nt Function: noun Date: 1611 1 : the act or process of displacing : the state of being displaced 2 a : the volume or weight of a fluid (as water) displaced by a floating body (as a ship) of equal weight b : the difference between the initial position of something (as a body or geometric figure) and any later position c : the volume displaced by a piston (as in a pump or an engine) in a single stroke; also : the total volume so displaced by all the pistons in an internal combustion engine (as in an automobile) 3 a : the redirection of an emotion or impulse from its original object (as an idea or person) to another b : the substitution of another form of behavior for what is usual or expected especially when the usual response is nonadaptive
