General Terms:
* Silent: This is a neutral term describing someone who doesn't speak.
* Quiet: Similar to silent, but can also imply a preference for solitude or introspection.
* Reticent: This suggests a reluctance to speak, often due to shyness or a desire for privacy.
* Reserved: Similar to reticent, but can also imply a more deliberate and controlled approach to communication.
Specific Situations:
* Mute: This term is typically used for someone who is physically unable to speak. However, it can sometimes be used metaphorically to describe someone who chooses not to speak.
* Vow of Silence: This describes someone who has taken a religious or spiritual vow to abstain from speaking.
* Introvert: While not directly related to speaking, introverts often prefer to listen and observe rather than talk.
* Selective Mutism: This is a psychological disorder where someone can speak in some situations but not others, usually due to anxiety.
Informal Terms:
* Tight-lipped: This suggests someone who is unwilling to share information.
* Mum: This is a British term for someone who is silent or unwilling to speak.
* Quiet as a mouse: This is a playful way to describe someone who is very quiet.
Ultimately, the best term to use depends on the specific situation and the reason why the person chooses not to speak.