efficient market
noun[S]
ECONOMICSukusamarketwhere all theimportantinformationisavailableto everybodyinvolvedat the sametime, andpriceschangeimmediatelyaccordingto thisinformation:
In anefficientmarket,pricesreflectallavailableinformation, and so pastpricescantellyou nothingusefulabout whetherfuturepriceswill go up or down.