Shares in a no-liability company which are forfeited (lost) to the previous owner because of non-payment of a call on the shares.

forefieted shares means which unpaid by the investor to 
alloted shares. these are again sale to public is known as 
forefieted shares or buyback shares.

when an investor do not pay the allotment amount and just pay only one installment of stock price i.e. 1st price. then company will give call i.e. 1st call, 2nd call to the investor about the amount. even then the investor do not pay the amount . then the company will take back those shares. Along with that the amount paid by investor will not be returned to investors. such shares which are taken back by the company is called forefieted shares.