A bid designates a number of odd tricks (tricks in excess of six), from one to seven, and a denomination. (Pass, double and redouble are calls but not bids.)
A bid supersedes a previous bid if it designates either the same number of odd tricks in a higher-ranking denomination or a greater number of odd tricks in any denomination.
A bid that supersedes the last preceding bid is a sufficient bid.
A bid that fails to supersede the last preceding bid is an insufficient bid. It is an infraction to make an insufficient bid (see Law 27 for rectification).
The rank of the denominations in descending order is: no trump, spades, hearts, diamonds, clubs.
Regulating Authorities may authorize different methods of making calls.