What does _ underscore mean when used in a sentence or separating words?
In modern usage, underscoring is achieved by markup or with combining characters. The original free-standing underscore character continues in use to create visual spacing within a sequence of characters, where a whitespace character is not permitted (e.g., in computer filenames, email addresses, and in Internet URLs). In contexts where no formatting is supported such as in instant messaging, or older email formats, the 'enclosing underscores' markup is sometimes used as a proxy for underlining the word(s) enclosed (thus).