Trapezoidal, actually. But the square sails were called square sails. Lateen or square could be referred to as yards.
They were referred to as "four-cornered" sails.
I'm not an expert, but I believe you can sail closer to the wind with a lateen-rigged sail than with square sails.
The lateen sail was used at the same time a square sail was used, but has different uses. The square sail is fine if you have a heavy boat and always fiind a wind that is blowing in the direction you want to go. Under such conditions, a lateen sail isn't much of an improvement. It was only once boats were made lighter (to faster get from the Atlantic to the Orient) that the triangular sails were an advantage. Also, if the wind is often blowing sideways to the way you want to go, a square sail, even if angled, doesn't work as well as a lateen sail. A triangular sail actually has a bit of lift to it so you can point your boat closer to the eye of the wind and still sail. This makes it ideal for sailing in and out of harbors and along the coasts. So small boats orginated the lateen sail for dexterity.
The solid shape that has one square face and four triangular faces is called a pyramid. If you were to have a shape that had four triangular faces and no square face, it would be called a triangular pyramid.
None, because there can be no such thing as a triangular square. If it is triangular it cannot be a square, if it is a square it cannot be triangular.
Uper-triangular Matrix A square matrix A whose elements aij=0 for i>j is called upper triangular matrix.
A triangular pyramid has a triangular base and three triangular faces meeting at its apex. A square pyramid has a square base and four triangular faces meeting at its apex.
Square Pyramid has a square base and 4 triangular sides. Triangular Pyramid has a triangle base and 3 triangular sides.