OOC stands for out of character. If you see this in game, it means that a player is speaking to you as a player, not character to character.
This type of communication is discouraged, unless it is to direct a player to support resources, or to enquire about adult consent for explicit roleplay. It is recommended to use it in whispers only, to respect the game immersion of the players.
OOC should not be used on radios as this can be disruptive to large numbers of players. If you witness bad behaviour on the radios, you should report it immediately to the Players Department, and allow them to give guidance to other players.