A fairly common phrase heard on the course after a poor shot "I'll declare that ball lost". The problem is that this has no meaning within the rules - under Rule 18.2a the only time a ball is lost is when it is "not found in three minutes after the player or his or her caddie begins to search for it".
If a ball is discovered within the 3 minute search time and identified as the player's ball, then that ball is not lost and it is the ball in play unless a provisional ball has been played from "Spot Nearer Hole Than Where Original Ball Is Estimated to Be".
There is no requirement to go and search for your ball, so you can abandon it. But just saying that you want it to be lost does not make it a lost ball.
