The dollar sign ($) and the underscore (_) characters are JavaScript identifiers, which just means that they identify an object in the same way a name would. The objects they identify include things such as variables, functions, properties, events, and objects.

详细请进行学习jQuery，大概一个月时间，虽然现在用到不多，但是也会经常遇到，因此还是有必要进行学习。

官网进行学习： 直达： https://learn.jquery.com/using-jquery-core/dollar-object-vs-function/