Refers to all four sides or directions around something; often used in expressions like 四面楚歌 (surrounded by enemies on all sides).
The building has glass on all four sides.
He found himself surrounded by enemies on all sides.
四方 also means 'all sides' or 'four directions', but is more common in everyday spatial descriptions, while 四面 often appears in set phrases or formal contexts.
Composed of 四 (four) and 面 (face, side). The reading しめん is the standard on'yomi combination.