A bidding system is the complete set of methods in a partnership to describe the meanings of calls. It includes treatments, conventions to deal with both constructive auctions and competitive auctions. The details of the bidding system must be known to the opponents.
Common systems are
- 2/1 game forcing
- Bridge World Standard
- Standard American
- Standard American Yellow Card
A bidding system is called natural if it contains mainly natural calls. They are not only used by beginners, but also lots of experts. The most common systems are Standard American, 2/1 game forcing and Acol.
Even a natural system contains some artificial calls, which are called conventions.
An artificial system is a system which is mainly composed of highly codified artificial calls. Examples include Relay systems.