Active Contingent means they have offers in on them which have not yet been accepted by the seller.
When the status is marked Active Contingent Short Sale, it means they have offers on the property, signed by the seller and sent to the lender for approval.
Normally this means your offer would be a back up.
If the selling agents are being ethical they'll give the 1st buyer to put in an offer the chance to meet the banks counter offer before moving on to other buyers who put in offers after the first one.
So ideally you want to make your offers on Active properties if you can.
Buyers fall out for all kinds of reasons. If it' a property you like, make an offer...get it in the hopper!
I recently closed a great deal on a house for a couple moving here from Ohio, our offer was in as a back up and the first buyers walked!!! We replaced thier contract with the lender and were ready to close in a week!