A website, when the job is to be found and trusted
If customers need to find you, understand what you sell and get in touch, a fast, well-structured website that your own team can update is the answer. In Saudi Arabia that usually means Arabic and English versions, built for phones first.
A web application, when the job is work
Bookings, orders, records, portals for clients or staff: anything people log in to and act on. A web application runs in any browser, needs no app store, and is updated once for everyone.
A mobile app, when the work happens away from a desk
Drivers, technicians, sales teams, parents: people who create or need information on the move, sometimes without a signal. A mobile app can work offline, use the camera and location, and send notifications.
How to decide
Start from the task and the person doing it. If it is reading, it is a website. If it is doing, at a desk or anywhere with a browser, it is a web application. If it is doing on the move, it is a mobile app. Many businesses grow from the first to the third over time, on the same records.