It is an approach where the result of one function is passed on to the next function, which is passed to another until the final function is executed for the final result.
//example
const double = (x) => x * 2;
const square = (x) => x * x;
var output1 = double(2);
var output2 = square(output1);
console.log(output2);
var output_final = square(double(2));
console.log(output_final);