If it has a 72 hour release clause and another offer comes in, the seller must notify the buyer that they have accepted another offer the the buyer has 72 hours to remove their contingency or the seller will go with the new offer.
NOTE: It's usually 72 hours, but it can be negotiated to shorter or longer terms.
These are the Status Definitions taken directly from the MLS website, I hope this helps.
Status Abbreviation Definition
Active A Valid listing contract exists and no offer accepted.
Pending with Release, continue to show PR Accepted offer on the property â€“ a release, â€œescapeâ€ or â€œkick-outâ€ clause exists in a purchase contract that allows one party to withdraw under certain circumstances. This status may also be used to indicate the property is a Short Sale with an accepted offer.
Pending without Release, continue to show PS Accepted offer on the property, still showing to prospective buyers for offers in back-up position to the first accepted offer.
Pending Do Not Show PN Accepted offer on the property. No additional showings to solicit buyers.
Sold S The Final Sale has occurred.
Expired E Listing Contract has Expired.
Canceled C Listing Contract Canceled, or Listing is not qualified for inclusion in MLS.
Withdrawn W No longer on the MLS, but a valid contract exists with the Listing Broker. Temporarily Off-market.