noun · a rear entrance to a building, gate, or structure

他忘了锁后门。

noun · the use of personal connections or under-the-table dealings to gain an advantage

他是通过走后门才得到这份工作的。

noun, punctuation · the opening at the end of the alimentary canal through which solid waste leaves the body

这种退烧栓剂需要塞入后门，这样药物成分吸收得更快。

noun · a hidden entry point in a computer system or software that bypasses security checks

黑客在服务器上植入了一个后门。