歇后语，An idiomatic two part double pun. Part one is akin to a riddle, while part two is usually a double pun based on part one. The second part is often omitted.
Examples:
皇帝女 Emperor's daughter ——不愁嫁 not worry to find a husband；
Iphone是皇帝女。
Iphone is like emperor's daughter. (never be worried about overstocking)
肉包子打狗 Using the meat bun to hit a dog —— 有去无回 It will be lost forever ；
你借钱给那个骗子，简直是肉包子打狗。
You lend the money to that swindler, it's certainly using a meat bun to hit a dog. (don't expect to get it back)
小葱拌豆腐Scallion with Tofu —— 一清二白 it's no doubt very clear；
这件事明摆着，小葱拌豆腐。
This case is obviously.
黄鼠狼给鸡拜年 Weasel says happy new year to a chicken —— 不怀好意 It's certain with an evil purpose；
他突然对你这么好，肯定是黄鼠狼给鸡拜年。
He appears very nice to you suddenly, it must be a weasel says happy new year to a chicken.
司马昭之心 Si Mazhao's evil ambition —— 路人皆知 that's transparent to everyone。
他的意图早已是司马昭之心，路人皆知。
He's intention is akin to Si Mazhao's evil ambition that was transparent to everyone.