If you need to explain your offer and collect enquiries, you need a website. If customers or staff must log in and do repeated work inside the product, you need a web application.
Choose a website when
You are publishing services, case studies, pricing context and a contact path. SEO, speed and clarity matter more than complex user accounts.
Choose a web app when
People need dashboards, permissions, saved records, payments inside a workflow, or custom business logic. That is software, not a brochure.
Many businesses need both
A marketing site that explains the product, plus an application behind a login, is a common and healthy split. Build each for its job.