Scripts.start in package.json, what is it?

Hello, could someone explaint to me what is it this

  "scripts": {
    "start": "node app.js"

start property responsible for in package.json when I’m using node.js?

It’s so you can type npm run start to start your app.

Anything in the scripts section can be invoked with npm run that way, and the nice thing about it is it looks for executables in .node_modules/bin first.