区 is built from the 匚 (box (open right)) and 乂 (crossed / mow) components.
It belongs to a phonetic family with 欧 and 殴 — they share the 区 component and the reading オウ.
A common word using 区 is ~区 (~く), meaning “~ district, ~ ward, ~ borough”.
Kanji that look similar include 匹 and 匠.