"Idiomatic" coding following the conventions of a given language. It is the most concise, convenient, and common way of accomplishing a task in that language, rather than forcing it to work in a way that you are familiar with in a different language.

Awkward:

if (out === "") {
  // blah
}

Awkward:

if (out === undefined) {
  // blah
}

Idiomatic:

if (!out) {
  // blah
}