Triangulum is a Northern Hemisphere constellation otherwise known as the Triangle. It is one of the 48 Greek constellations originally described by the 2nd century astronomer Claudius Ptolemy (Wikipedia). Triangulum remains one of the 88 modern constellations defined by the International Astronomical Union (Wikipedia).
Triangulum (abbrev. = Tri; genitive = Trianguli) covers 132 square degrees or 0.32% of the celestial sphere making it the 78th largest constellation. It contains 25 stars brighter than apparent magnitude 6.5, the brightest star being Beta Trianguli.