Static vs dynamic websites
Static sites serve pre-built pages, so they're fast and secure; dynamic sites build pages on request, so they're flexible and interactive. Most modern sites blend both.
The difference between a static and a dynamic website is when the page gets built.
Static
A static site serves pages that were built ahead of time. When someone visits, the server hands over a ready-made file. Because nothing has to be assembled on the spot, static sites are typically very fast, secure (less to attack), and cheap to host. Brochure sites, landing pages and marketing sites are often best as static.
Dynamic
A dynamic site builds each page on request, often pulling from a database: think a logged-in dashboard, a booking system, a shop showing live stock. This makes them interactive and personalised, at the cost of more moving parts to host and maintain.
The modern blend
The line has blurred. Modern tools let you pre-build most of a site for speed, then layer in dynamic pieces only where they’re needed: fast by default, interactive where it counts. This is the approach behind a fast site with a CMS: edit content easily, serve it quickly.