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.
Square sails are not truly square but rectangular with a longer long side on the bottom perimeter of the sail. They were and are referred to as "four-cornered" sails.
Triangular-shaped sails helped catch wind from the sides and rear.
"Square-riggers" have primarily square sails, but the jib sails are triangular.
Square sails are square
One type is the "lateen sail", but there are also jibs; Genoa & spinnaker.
Lateen sails were adapted from the Mediterranean region.
The triangular sail was invented beginning in the 16th century. They were first seen in the Mediterranean as single yarded lateen sails.
Square sails (rectangular) were (are) called four-cornered sails.
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