HHP is a popular online abbreviation for “haha point”. "Haha" is an echoic word for laughter in Chinese and "point" is the Chinese equivalent of "threshold." Therefore, haha point refers to the threshold where you can be amused and burst into laughter.

HHP是网络上流传的“笑点(haha point)”这个词英文说法的缩写形式。Haha(哈哈)是汉语中形容笑声的象声词，point(点)在汉语中指“门槛”或“基准线”。那么，“哈哈点”(即“笑点”)指的就是能够让你发笑的那个点。

If we say someone has a quite low haha point, that means he can be very easily amused.

如果我们说某人的笑点很低，那就是说这个人很容易被逗乐。

在医学中，“痛点”就是用pain point来表示的，估计这个haha point也是从这里衍生而来的吧。