Here are some other terms that may be used:
* Frame: This is a more general term for a single unit of a visual narrative, and can be used for comic strips, but also for other forms of art like film.
* Cell: This term is more common in animation, but can also be used for comics, especially when referring to individual images in a sequence.
* Box: This is a less formal term, but is sometimes used in casual conversation.
The most common term, however, remains panel.