Use Tiny Variable Names

When scope is small and meaning is exceptionally well understood.

Dialectic

Use when the scope is tiny. Use when the scope is massive and you reference it a lot. Use when the meaning is well understood, such as i for "index", or xVel for "velocity along the x axis". Use when long names would distract from the structure of a complex expression, such as in Math: sqrt(a**2 + b**2).

Don't use when other people will need to read, check, and comprehend your code. Don't use when you have unlimited space. Don't use when you're tired of typing.

History

In the history of JavaScript, jQuery used the dollar sign $ as a single-character variable, and Underscore used (you guessed it) the underscore _.