A box used to pack mikan (mandarin oranges). They can be identified by the characters "みかん" or by an orange printed on the box.
The mikan box is a recurring trope in anime and manga, with a disproportionate fraction of all cardboard boxes being mikan boxes. It's sometimes used as makeshift furniture to illustrate a character's poverty, or as a box where unwanted pets are given up for adoption by the side of the road.
