Anything that looks like a a shape with three sides and three angles is triangular. If you see a triangular fin in the ocean while you’re swimming, watch out! Shark!
Start looking for triangular shapes and you'll begin to see them everywhere, from a triangular slice of pizza to a tortilla chip. Like triangle, triangular is rooted in the Latin tri-, "three," and angulus, "angle or corner." You'll also occasionally find this adjective describing things that involve three people, like a triangular relationship between three best friends.