“敲门砖”，字面意思指“拣来敲门、门开后即被丢弃的砖头（brick picked up to knock on the door and thrown away when it has served its purpose）”。常用来比喻世人借以猎取功名的工具（thing used as a means for fame and position），一达目的，即可抛弃。
与“敲门砖”意思相近的表达还有“垫脚石”，两者都可以翻译为“a stepping stone to success”。
例句：
有些人常把读书当成“敲门砖”，一旦功名到手，书籍也就被束之高阁了。
Some people take attending to school only as a stepping stone to status; once they succeed, all the books will be shelved.
他甘愿当垫脚石。
He is willing to be a stepping stone.
（中国日报网英语点津 董静）
