1A men's business suit — a matching jacket and trousers worn for work or formal occasions. Somewhat old-fashioned; in everyday conversation スーツ is the default, but 背広 is still used by older speakers and in newspapers, novels, and other written contexts. 背広 is ateji.
父はいつも紺の背広を着て出勤する。
My father always wears a navy suit to work.
結婚式に着ていく背広をクリーニングに出した。
I took the suit I'm wearing to the wedding to the cleaners.
祖父は若いころに買った背広を、いまでも大切に着ている。
My grandfather still treasures and wears the suit he bought when he was young.
古い写真には、背広姿で微笑む祖父が写っていた。
In the old photo, my grandfather was smiling, dressed in a suit.