They are referred to as four-cornered sails.
They were referred to as "four-cornered" sails.
Square sails are square
I don't think there is another name other than blade.
Square sails are referred to as four-cornered sails.
Trapezoidal, actually. But the square sails were called square sails. Lateen or square could be referred to as yards.
"Square-riggers" have primarily square sails, but the jib sails are triangular.
"Square sails" which are not really square, were/are referred to as four-cornered sails.
"Four-cornered" sails were (are) square.
Square sails (rectangular) were (are) called four-cornered sails.
Square sails are referred to as four-cornered sails.
Historically, they are referred to as "four-cornered" sails.