Reentrant or re-entrant can refer to:

• Re-entrant (landform), the low ground formed between two hill spurs.
• Reentrancy (computing) in computer programming
• Reentrant mutex in computer science
• Reentry (neural circuitry) in neuroscience
• Salients, re-entrants and pockets in military tactics
• Reentrant tuning in music
• Concave polygon, AKA reentrant polygon

• Reentry
• Reentrant dysrhythmia, a type of cardiac arrhythmia