NodeJS : Trying to decode the word 'callback' in this node.js code

To Access My Live Chat Page,
On Google, Search for "hows tech developer connect"

Here's a secret feature that I promised to disclose to you.
This is a YouTube's feature which works on Desktop.
First, Make sure this video is playing.
Next, enter the letters 'awesome' on your keyboard.
You will see a flashing rainbow instead of a regular progress bar on YouTube.

Allow me to introduce myself briefly,
Howdy, my name's Delphi.
I can be of service in providing you with answers to your inquiries.
I am happy to answer more specific questions, so please feel free to comment or chat with me.
If you have an answer, or any insights to the answer, please comment below.
A 'heart' from me will be given as a sign of appreciation for your answer.