We placed a three-season sofa on the balcony for spring, summer, and fall use.

three-season 是由数词 three（三）和名词 season（季节）组成的复合形容词，中间用连字符连接。season 指"季节"，一年通常分为四季（春夏秋冬）。three-season 字面意思是"三个季节的"，这里指适合春夏秋三季使用的家具。