Boxy differs from oversized: an oversized piece is simply bigger all over, while a boxy piece has specific proportions — shorter body, wider cut, often a straight hem — that hold their shape rather than draping. The result sits away from the waist instead of tapering in.
Boxy tops pair naturally with higher-waisted bottoms, since the cropped length shows a sliver of waistline and keeps the proportions from looking blocky.