What is this called and how do I make one? Plus Button in Red Box

From within the CRM under “Create Account”. The Email Address field has a + (Plus) button in a reddish box.

What is this reddish box with the Plus sign in it called and how do I make one for a custom field?

It’s an awesome little button/feature because I can add Email addresses to my heart’s content without having to create a field for each email address (i.e. email_1, email_2, email_3, etc)

Here’s my end-goal:

I have a list of businesses. I’d like the Account record to include a list of products each business sells. The ideal design would be a TextField titled “Products:” with a reddish Plus box that would allow me to add a number of products as I go along.

My work around right now is to create the following fields:

… and so on until I get bored of creating fields.

Thank you in advance.
p.s. I’ve scoured through the docs, searched the web, looked for videos on YouTube, and frankly I don’t know what I’m looking for.

See this thread, there is a free add-on that helps with this