A "trucker hat" is a type of baseball cap or hat commonly worn by truck drivers. It typically has a mesh back and a foam front with a curved bill. Full definition
NGC 3310 Starburst Galaxy Trucker Hat with beautiful Astronomy and Space picture is a great Astronomy and Space gift (cafepress.com)
NGC 4414 Spiral Galaxy Trucker Hat with beautiful Astronomy and Space pictures - a great Astronomy and Space gift - by Spacemart, a Hubble Space Telescope Online Giftshop (cafepress.com)