What does the Twitter hashtag #壕 mean?
It is a currently popular Internet slang in mainland China.

壕 =&gt; short for 土豪 noun =&gt; &quot;local tyrant&quot;, someone who has much money.

壕/土豪 is used in a joking occasion, it doesn't mean the person it describes should actually have much money.
Example

A: 我昨天买到了iPhone 5S！ I bought iPhone 5S yesterday!
B: 土豪土豪我们做朋友吧！ Tuhao tuhao, let's make friends! (Note: A and B are already friends. That B says so is just to make fun. It is like another expression &quot;你真有钱啊！&quot;. But it doesn't mean B really thinks A has much money.)

EDIT
百度百科【土豪】 has well summarized this word:


指“暴发户”。It means &quot;nouveau riche&quot;.

指网络上无脑消费的人，也可以引申到其他领域（网络游戏、电子设备、动漫ACG等）。如某网络游戏中的人民币玩家被称为“土豪”，有时也会简化为“壕”。 It means someone who spends money mindlessly on the Internet. And its meaning can extend to other areas ([mindlessly spending money on] online games, electrical devices, or Animation/Comic/Game etc). For example, in an online game, the P4W (pay-for-win) players are called 土豪, sometimes using the short form &quot;壕&quot;.

用于讽刺那些有钱又很喜欢炫耀的人，尤其是通过装穷来炫耀自己有钱的人。该意义衍生出“土豪，我们做朋友吧”等句子。 It is used to satirize those who have much money but like showing off -- especially those showing off by pretending to be poor. For example, &quot;土豪，我们做朋友吧&quot;.

土豪的思想境界文化水平一般都不高，知识面却异常宽泛，但都是了解皮毛之辈。 Generally, 土豪 have low ideological and educational level, but broad scope of knowledge.

有些人把比自己肯花钱的人都称之为“土豪”。 Some would call those who are more willing to spend money than themselves &quot;土豪&quot;.

土豪说简单点就是很土的富豪。 In short, 土豪 is rustic but rich people.



As an Internet slang, 壕/土豪 is very informal and its definition cannot be rigorously stated. So it's better to use it only in spoken language or on the Internet.