A camp shirt or lounge shirt is a loose, straight-cut, short-sleeved shirt or blouse with a simple placket front opening and a "camp collar" - a one-piece collar (no collar band) that can be worn open and spread or closed at the neck with a button and loop. It usually has a straight hemmed bottom falling at hip level, not intended to be tucked into trousers. It is often the base for fancier fabrics such as bowling shirts, aloha shirts, or various other Hawaiian/tropically inspired weaves and patterns.
References
Camp shirt Wikipedia(Text) CC BY-SA