What is isolation level in SQL?

Short answer: The isolation level in SQL defines how transactions interact with each other in terms of visibility of data. The isolation level affects the balance between data consistency and transaction concurrency.

Real-world example (ShopNest)

Checkout wraps stock decrement + order insert in a transaction so you never sell stock you do not have.

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.