a three-sided polygon
"The children drew a triangle on the paper to represent their new game board."
something approximating the shape of a triangle
"the coastline of Chile and Argentina and Brazil forms two legs of a triangle"
a small northern constellation near Perseus between Andromeda and Aries
"The ancient mariner pointed to the faint triangle in the night sky, noting its position just above the river of milk that flowed through Andromeda."
any of various triangular drafting instruments used to draw straight lines at specified angles
"The student placed a triangle on the paper to ensure her diagram had perfectly accurate ninety-degree corners."
a percussion instrument consisting of a metal bar bent in the shape of an open triangle
"The drummer struck the gleaming metal triangle with a small hammer to add a crisp, high-pitched sound to the orchestral piece."
A polygon with three sides and three angles.
"The surveyor drew a triangle on the map to mark the boundary of the forest."
In plain English: A triangle is a flat shape made of three straight lines that connect to form three corners and enclose an area.
"The children played tag by forming a human triangle in the yard."
Usage: Use this term to describe any flat shape formed by connecting three points, whether in geometry or when referring to the triangular arrangement of people or objects. Avoid confusing it with a pyramid, which is a three-dimensional solid that tapers from a base to an apex.
The area comprising the cities of Raleigh, Durham and Chapel Hill in North Carolina. Used with "the" except when attributive.
"The Triangle has seen a surge in tech startups over the last decade."
The word "triangle" comes from the Latin triangulum, meaning "three-cornered." It is formed by combining the prefix for "three" with a word for "corner" or "angle."