Visual contact was a term for describing when something was visible.
In 2265, as the USS Enterprise approached the disaster recorder of the SS Valiant, Captain James T. Kirk asked navigator Lee Kelso, "No visual contact?" Kelso respond, "No, sir." (TOS: "Where No Man Has Gone Before")
In 2366, sensors aboard the USS Enterprise-D indicated the approach of a Borg vessel but there was no visual contact. Captain Jean-Luc Picard ordered Worf to use their current viewscreen magnification to view fifty degrees starboard and there was still not visual contact. (TNG: "Evolution")