As an opening Edit
A 3♠ opening is preemptive in every system.
As a response Edit
The 3-level responses of a 1NT opening have many possible meanings, which depend on agreements.
A single raise of a weak two bid is preemptive and to play.
This shows a strong hand and a self-sufficient suit, and is forcing.
As an overcall Edit
A jump overcall of 3♠ is usually equivalent to a 3♠ opening, which is preemptive.