What is the difference between mutable and immutable objects?

Short answer: Mutable: Can be changed after creation (e.g., arrays, objects). Immutable: Cannot be changed once created (e.g., strings, numbers).

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.