There are 2 words for a shelter like this. Since it's open on all sides, call it a 'canopy'. If it were split slanted sides like a tent or closed on one side, it'd be more of a 'bivouac shelter' (pronounced "biv-oo-wack"), which is just a primitive sort of tent, not to be confused with 'bivouac sack' which usually is more of a primitive sleeping bag.