Bids are Coded Messages that CHANGE !
As the bidding process advances, the meaning of a bid (and what information is transmitted) changes depending upon the bid that preceded it. This web site explains the meaning of the coded messages as they change as the bidding process progresses.Final Bid is the CONTRACT
The bidding process is like a normal auction, that is the various participants making ever increasing bids on an item. The highest bidder wins the item. In this case the bidders vie for a "CONTRACT", hence the name of this card game, Contract Bridge. The contract is the commitment by the partnership to take a certain amount of the 13 tricks using one of the 5 strains.