Software built for a single industry — restaurants, construction, dental clinics, trucking — as opposed to horizontal tools that serve every industry shallowly. Vertical SaaS wins through deep workflow coverage, industry-specific compliance, and the ability to layer in payments and financial services as a second act. Canonical examples: Toast (restaurants), ServiceTitan (home services), Procore (construction). A recurring topic in Gokul Rajaram's moats framework.