Smoke tests are run after deploys or big changes. They answer whether the app starts, key pages load, and critical flows still function at a basic level.
ELI5
Think of Smoke Test as a simple recipe for doing the work better. A quick check that the most important parts of an app are not obviously broken.
In practice
Use it when you need a repeatable method instead of guessing from vibes. In practice, define the owner, input, output, and failure mode before you rely on it.