To you as a buyer interested in the property, it means that the seller can not accept any offer you give them regardless of the price/terms unless the initial offer/buyer backs out on his/her own accord and the property becomes "active" again (pending release).
DISCLAIMER: This is not intended as legal advice. Every contract is different. Consult an attorney for guidance.
The most basic difference between KICK OUT clause and NO KICK OUT clause is WHO controls the contract: the Seller or the Buyer.
Once the offer is ratified:
1) Kick out clause - Seller can void the contract and accept another offer
2) No Kick out clause - Buyer can void the contract based on one of the contingencies written into the contract; Seller cannot void the contract without Buyers consent.
It all depends on the way the contract is written.
Most contingencies come wtih a no kick out clause, such as home inspection, radon, finance, appraisal, etc.
But, If the buyer requested a contingency so they try and sell their own home, it would most probably have been a contingency with a kick out clause.
Hope that helps