How to split the Run Tool Window in IntelliJ IDEA?

As far as I know the h/v split feature is available only for editor tabs. There's also a split mode for tool windows but it works only for different windows, not for multiple tabs of the same windows, so basically no you can't, and I can't imagine what was the reason behind this choice.

You have to right-click on the terminal tab choose "Move to Editor". Then in the editor, you can split editor tabs vertically or horizontally to have more than one terminal in a column or row. Your answer is discussed (here) as well.

You can't split runs, but you can open build in a terminal and split/stack them in any combination. It's not like a one-click run solution, but can be splited/stacket. Hope somebody found it useful.

Tip: you can copy command from the run tab and paste to the terminal so you don't need to type it.

IntelliJ Ultimate 2018