SpringHeeledJack,
Apart from calling it a "background process", you are along the right lines. Interpreted scripting languages don't run as background processes, they are parsed and interpreted on demand by a plugin for the web server software (which is the background process that listens to port 80 and talks back to your web browser).
Other than that, you're along the right lines. On a website with a content management system (which is essentially what you're describing), the designers create a template with editable regions. Then scripts written in whatever language are used to insert content into the regions and to call it up on demand based on what page you are on (typically the content is stored in a database, making the website fully dynamic apart from the static template).