Your car has an exterior (paint, tires, sun-roof, mirrors) and interior (engine, transmission, electrical, fuel).
Your website is the same basic concept. The exterior is what your customers or viewers see, the interior is what runs the website.
Just like you would wash your car to make it all nice and shiney and do monthly preventative checks (oil and water levels, belts and cables), you do the same thing for your website.
Exterior is all about content updates making sure all your content is relevant to your viewers and easy for them to navigate through.
The interior is the WordPress platform, theme, visual builder and assorted other plugins that make up your website. It’s the as needed backups in case something unexpected happens with a major update; and the uptime montioring so you know that a vital part of your marketing strategy is functioning at full capacity.