I saw that on reddit. On thye official clasisfication for the Grand Prix, the second to last column is 'ON'. Seems to be something relating to laps, but I can't figure out what.
So what is ON in official F1 Classifications?
The "ON" column shows which lap that driver set their fastest lap. E.g. Hamilton set his fastest lap of 1:32.764 on lap 53.
LAPS - Laps completed - the race ends when the first driver crosses the line. All subsequent drivers complete their race at the end of the lap that they're running. Races can also be terminated on a duration basis (x amount of laps or y number of minutes, whichever is sooner (the vast majority of the time, it's on laps though))
TIME - Total elapsed race time
GAP - Difference in time between leader finishing and this driver's finishing time
INT - Difference in time between this driver's finishing time and the driver ahead
KM/H - Average speed for the duration of the race
FASTEST - Fasted lap time achieved for this race
ON - Lap number of the fastest lap for this driver
PTS - Championship points awarded for this driver for this race.