Post-Only
Bybit describes Post-Only as an instruction for a limit or conditional limit order to be placed on the order book only if it would not execute immediately. If the order would immediately match, it can be cancelled instead, helping the trader avoid an unintended taker execution.
Reduce-Only
Reduce-Only is designed to reduce or close an existing position and not increase or reverse the position. It is commonly used for closing or take-profit limit orders where an accidental opposite position would be undesirable.
Shortcut: Post-Only is mainly about maker/taker execution behavior. Reduce-Only is about preventing position size from increasing or flipping direction.
Official Bybit references
Reviewed against Bybit's current help-center explanations.
Post-Only Order →Reduce-Only Order →