Preemptive Bids

Preemptive bids include both openings and overcalls.
The difference is only that the opponents opened first.

Preemptive bids of all kinds are used a lot in competitive-level
bridge -- far more than in social bridge.  They start at the two
level and go up to the 6 and even 7 level.

You must become comfortable or even agressive at preempting,
and you must become comfortable bidding over opponents'
preempts, because both are necessary to win at duplicate.