部(bù) - part, section; ministry; measure word for films and machines in Mandarin

部 (bù) is a workhorse morpheme rather than a word you often say on its own. It carries the idea of a division: a part of something (全部, 部分), a department of an organisation (部门), a wing of the army (部队), or a ministry of state (教育部, 外交部).

It is also a measure word, used for long works and substantial machines: 一部电影, 一部小说, 一部手机, 一部电梯. The flavour is weightier than 个 and it suits things with internal structure, which is why it takes films and novels but not photographs.

Two traps. First, it is not the general word for "part": that is 部分, and 这个部 on its own means a department, not a piece. Second, do not confuse it with the negative 不 (bù); they share a sound and a tone but nothing else, and only the character keeps them apart on paper.