Wikipedia
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.
Usage examples of "camp shirt".
I will never, as long as I live, she promised herself faithfully, daubing ointment on the worst of the scrapes, wear shorts and a camp shirt to another war.
She knew how she must appear, in waterlogged jeans and camp shirt, not in the least pretty or delicate or curvaceous in the way that seemed to attract the opposite sex.
To the liquid jarring of her breasts beneath the blue camp shirt that made him wonder how they would feel .
But really, this disheveled boy in camp shirt and boating culottes didn't much resemble the Bascal Edward you saw on TV.
She was wearing the navy-and-white striped slacks he'd bought her, with a white camp shirt tucked into the waist.
The house was quiet when she came downstairs, freshly showered and comfortable in olive-drab cotton slacks and a camp shirt.