How does 'CONCATENATE_SCRIPTS' work on wp-config?

The text on my wordpress text editor is white on a white background so its invisible for most people..

I searched it and the solution I found was to add the following code to wp-config.php

define('CONCATENATE_SCRIPTS', false );

It worked fine but I couldn't find what it does or why it works.

I only found a question that asks the same thing here but it didn't get an answer.

Could someone explain what the code above does and why it works?

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