A school trip or group outing/ excursion (commonly a school event where students bring boxed lunches).
明日は小学校の遠足で、みんなで公園に行きます。
Tomorrow is the elementary school's field trip; everyone will go to the park.
遠足の日はお弁当を忘れないようにしてね。
Don't forget your lunch on the day of the field trip.
会社の親睦遠足でハイキングに行った。
We went hiking on a company outing to build camaraderie.
A (dated) term for a long walk or excursion on foot.
昔の旅行者は山々を歩いて遠足することが多かった。
In the past, travelers often undertook long walking excursions through the mountains.