Is there a good example (and name) of a floating button which appears between rows/columns?

Question

I'm imagining a way of inserting a new row or column, where when the cursor approaches the outer vertex of a row or column (where the divider meets the outer edge), a button with a + appears allowing a new one to be inserted there.

Here's a mockup I made to demonstrate my idea:

Are there any real-world examples of apps that do this? Additionally, what is this called?

Answer 1

A number of website builders use this pattern to allow users to insert content between blocks. Take SquareSpace:

Answer 2

I would say it is just a button or according to Google Material a Floating action button.

Image source: https://material.google.com/layout/principles.html#principles-floating-action-button