Autumn trees on the background of the river surfaceAutumn trees on the background of the river surface
The setting sun, going beyond the edge of the forest, is reflected in the water surfaceThe setting sun, going beyond the edge of the forest, is reflected in the water surface
В математике: граница, отделяющая геометрическое тело от внешнего пространства. Наружная сторона чего-н..