Originally Posted by
Ttaskmaster
It's a means of entrance or access, in this case access to your mobo and other internals.
It will still have a frame around it to which the panel attaches, so the entirety is not removed.
It is thus still a window.
There are some houses where the entire side opens up, though they are often only considered windows if glazed. Half the time they're considered doors, but so too are case panels that are hinged.
Actual noun depends on how many wittery buttery adjectives you use to describe these spectacular, innovative, high-class, contemporary, captivating, expressive features... or how up his own backside your architect is. Good ones will invent their own portmanteaus, usually from combining several French and Italian words in a breathtaking elucidation of syntactic gobbledygook...