Alternatively referred to as a low line, low dash, and understrike, the underscore ( _ ) is a symbol found on the same computer keyboard key as the hyphen. The underscore is commonly used as an alternative to the space key when the space is not allowed. For example, in computer programming, a variable may be named $my_variable since spaces are not allowed in a variable name.
How do I create an underscore?
Underscore and underline
An underscore is much different than an underline. If you're trying to underline any leter, number, or other text, the undline feature should be used.