a thin line in the surface of an object can be vertical, horizontal, or diagonal can be wide or narrow may have a sharp or rounded edge may have a uniform or varied width can be of any color
slit which is a thin line in the surface of an object slit which can be vertical, horizontal, or diagonal slit which can be wide or narrow slit which may have a sharp or rounded edge slit which may have a uniform or varied width slit which can be of any color