1. in geometry, a figure bounded by three lines, containing three angles, and having three points. If all three sides are equal, it is an equilateral triangle. If two sides are equal, it is an isosceles triangle. If all three sides are unequal, it is a scalene triangle.
2. anything having a triangular form; ie, a musical percussion instrument.
3. a group of three involved in some situation as one in which two women are in love with the same man, generally pointless - see: waste of time.