Taking an objective cleanly, with the pit under control and Smite ready for the last hit, so the enemy cannot steal it.
team chat
in full english
Secure the dragon first, then fight.
the context
"secure drake" or "secure baron" sets the order: the objective before the fight, not the other way round. "secured" confirms it is taken. The opposite of "steal": securing is what the team controlling the pit does, stealing is what the other one tries.