The rest operator in JavaScript allows a function to accept an indefinite number of arguments as an array, providing a way to represent variadic functions in JavaScript. It is denoted by three dots (...) as a prefix followed by the name of the parameter. The rest parameter must be the last parameter in the function definition, and a function definition can only have one rest parameter. The rest parameter syntax allows us to represent an indefinite number of arguments as an array.

The rest operator works by collecting all the remaining arguments passed to a function into an array. For example, if a function is defined with two regular parameters and one rest parameter, any additional arguments passed to the function will be collected into an array and assigned to the rest parameter. The rest parameter always returns an array, so any array methods that JavaScript provides can be used on it.

The rest operator is often used in combination with the spread operator, which allows an array to be expanded into individual elements. The spread operator is denoted by three dots (...) and can be used to spread the elements of an array into a function call as separate arguments.

In summary, the rest operator in JavaScript is a useful tool for working with functions that accept an indefinite number of arguments. It allows all remaining arguments to be collected into an array, which can then be manipulated using array methods.