A business suit (men's suit). An ateji term historically derived from 'civil clothes' or Savile Row; now commonly used to mean a suit.
明日は面接なので、せびろを着て行く予定だ。
I have an interview tomorrow, so I plan to wear a suit.
古い映画では背広を着た紳士が多く登場する。
Old films often feature gentlemen wearing suits.
背広は場所や場面に応じて選ぶのが大切だ。
It's important to choose a suit appropriate for the place and occasion.