What is the best term for a user interface showing large image or image gallery in a modal?
Two common use cases are e-commerce sites and photo galleries.
The first term that comes to mind is light box because the original JS library was so called and the terms seem to have made their way into the JS / web ecosystem, for example, "7 best WordPress Lightbox plugins" or "How to create a lightbox" .
One possible caveat is that "lightbox" usually means "a piece of user interface that is above the page, with the rest of the page grayed out". Even if the modal is very small, it is still a "lightbox user interface".
I liked the term "theater" mentioned here – it reminds me of something that takes almost full screen, which is good. However, I have never seen this term used in a user interface library / toolkit that I have never used, unlike for example "hero" (which is also "strange" but once you get used to it, it's clear and unique).