They got their child into this prestigious school through a back-door arrangement.

back-door 是由 back（后面）和 door（门）组成的复合词，字面意思是"后门"。 在英语中，back-door 常用来比喻"非正规的途径"或"不正当的手段"，类似于中文里"走后门"的表达方式。 back-door arrangement 指通过非正式或不合规的方式达成的安排。