An optical illusion depicting an impossible solid object made of three straight beams of square cross section which meet pairwise at right angles at the vertices of the triangle they form.

plural of love triangle

plural of isosceles triangle

plural of equilateral triangle

plural of acute triangle

plural of scalene triangle

plural of obtuse triangle

A right-angled triangular array of the natural numbers, whose generation is often set as an exercise in computer science education.

Used other than figuratively or idiomatically: see black, triangle. / (ufology) One of a class of triangle-shaped unidentified flying objects, usually with a light in each corner.

plural of Calot's triangle