Snapback means that the concessions that were agreed to by the pilots lapse and the wages and (sometimes) the workrules revert to what they were before the concessions.

Almost all post 911 concessionary contract amendments (LOAs) had snapback clauses. US Airways pilots did not, although the AFA (F/As) did have snapback language in their LOA. The East pilots got a 35 million dollar (split among the East pilots) payment in lieu of snapbacks.