Welcome to Stackoverflow 🙂

There are actually two things happening

DOING IT MANUALLY

1. Detect scrolling

The Images zoom in when they come into the Viewport. This can be done by waypoints.js

http://imakewebthings.com/waypoints/guides/getting-started/

2. Image Animation

It is not just the Image that is zooming in. Each Image is sitting in an together with some text and styled as a square tile.

You could use https://daneden.github.io/animate.css/ and here the zoomIn.

Both together might result in a very similar effect and be the easiest way for a beginner.

WORDPRESS PLUGIN

Note: I don’t know to much about WP

A quick search brought me to https://wordpress.org/plugins/animate-it/

It uses the animate.css and detects scrolling, seems to me well maintained, and is used more then 50,000 times.

I’d like to know what’s the name of the effect of images popping one by one.

Here’s an example: http://brandnew-hiphop.com/

What would it be called in terms of CSS animation?

This website currently uses WordPress was this effect custom built or is there plugins allowing me to recreate it?

Thank you for your help!