snake_case

Another common separator is the underscore (_). It's a symbol that looks the closest to a space. Often used with lowercase.

This is usually used when the evaluator is case insensitive where it would be confusing to use camel case, such as in APIs. You'll find body properties often in snake case.

GET https://movies.db?exclude_genre=horror,comedy

UPPER_SNAKE_CASE

As mentioned before, the uppercase can be used for keywords whose values will never change, also known as constants. An underscore can be used as a separator for it when multiple words are involved. This is sometimes called the upper snake case.

const HOURS_IN_A_DAY = 24;

double__snake__case

Another common variation is using two underscores between words. Just another way to separate words or group of words.

protip__do_this_sparingly