Certainty was the state of being absolutely sure or confident about something, having no doubt or question.
In 2364, Data told Jean-Luc Picard that he (i.e. the android) believe that the source of the malfunction was programmed to destroy any person moving in the hydraulics room, and Picard asked if it was certainty or speculation, to which Data replied that it was certainty. (TNG: "Home Soil")