Delta / triangle beside axsis in CNC modes ?

yesterday I was squaring up the ends of some long tube in CNC mode 9 running horizontal because of the length. I had no stop set so I had to touch off the end of each new part. I started up again this morning and forgot to rezero for the depth of cut on the new part in Y. I hit the green cycle button and knew I was off on the cut depth so I reach over to hit he red cycle stop button but hit the red feed stop button instead. In both mode 8 and 9 CNC mode hitting that button brings up the Delta / triangle symbol beside the X,Y and Z.
So far I have not found it in the manual.
What is that for?
Andy