How many stocks rose against how many fell on a given day, counted one company at a time rather than weighted by size. It is the check on a headline index number: a size-weighted index like the PSEi can close higher on two heavyweights while most of the market fell, and breadth is what exposes that split. A stock that posted no trade at all is counted separately, not as unchanged.
See every term in the full PSE investing glossary.