A website is generally informational — its purpose is to convey information to visitors: company profile, product catalog, articles, or contact information. Visitor interaction is limited, mostly just reading and browsing.
A web application is designed for more complex two-way interaction: users log in, enter data, process transactions, and the system responds dynamically. Examples include point-of-sale applications, online attendance systems, or financial reporting dashboards.
In terms of development complexity, web applications generally require database design, business logic, and user access management that are far more detailed than a regular website.
A simple way to determine your needs: if the goal is to display information and build your company's image online, a website is enough. If the goal is to manage day-to-day operational processes — transactions, customer data, reports — you likely need a web application.
It's also not uncommon for a business to need both: a website as a public storefront, and a web application as an internal operational tool.
