What are these "F,S,O" characteristic speeds?
F speed is the minimum speed at which flaps should be retracted from CONF 3 or 2 to CONF 1+F.
S speed is the minimum slats retraction speed, i.e. the minimum speed at which a clean configuration should be selected.
GD speed is the engine-out operating speed in clean configuration. In other words, it corresponds to the speed that allows the highest climb gradient with one engine inoperative in clean configuration.

source:
https://www.icao.int/WACAF/Documents/Meetings/2015/ICAO-BEA/SafetyFirstissue20.pdf