Don't overthink this - there's a very commonly used term and I ... have ... completely ... forgotten ... it ! ;-)
What is it called when a web page makes use of Javascript (generally in a sophisticated fashion that adds a significant amount to the functionality of the page) but things are arranged in such a way that if the browser has Javascript disabled the user is still able to gain some/all of the functionality intended (albeit perhaps with more effort / less eye-candy).
thanks
R.
The older term is graceful degradation. The newer, arguably more proper term is Progressive Enhancement. The distinction can be important, as it puts the emphasis on universal accessibility and universal functionality first, and enhancing the experience for those who can support it second.
The posters above me have given good terms, so I won't bother with that.
In case you were also asking about how it's actually done, the easiest way to do it is to use
<noscript>Alternative HTML here</noscript>
which is fine for little dinky things like displaying the time. For AJAX or JQuery-generated stuff, they need to have the full inner HTML for the element in question displayed first, which would then be wiped out (hopefully without too many graphical artifacts, if the page loads quickly enough) if JavaScript were enabled.
I'm sure there are other ways to do it, of course, but that's the basic idea-- provide in HTML an alternative to JavaScript, and if the JavaScript is supposed to look different, it can use the DOM or jQuery or whatnot to modify the HTML on the fly.