A vertical spread pairs a bought and a sold option of the same type and expiration at different strikes. Every vertical is defined-risk, and the four variants (bull put, bear call, call debit, put debit) are the building blocks most rule-based spread disciplines are built from.
The width between strikes sets the maximum outcome span: a credit vertical's worst case is width minus credit, a debit vertical's is the debit paid. Verticals compose: an iron condor is two verticals sold on opposite sides, and a broken-wing variant adjusts one width. Their package pricing (one net-limit order for the pair) is what keeps entry and exit costs predictable relative to legging in.