I've found something cool which I'd like to use in my project. Because I'm a pro and earn money with programming, I consider my own little project also to be "commercial". So this cool lib I have in mind has an "MIT-style license". Is that one something similar to GPL? Or more restrictive? Or less restrictive? It's an javascript library.
It basically means that you can do anything you want with that piece of code, you can modify it, distribute it and don't provide the source.
You can check the license here: http://www.opensource.org/licenses/mit-license.php
The only thing that it ask for is to keep the copyright notice provided with the license.
However you should be aware that the term MIT-Like license is not a specific license , it's just a family of similar licenses, so, you should read the specific wording of the license the software uses.
In short it literally means, you can do whatever you want with the source code as long as you keep the original author's name with the source code. It is more liberal than GPL and one of the most liberal opensource license.
The MIT license allows you to use the code in commerical software as long as you redistribute the license with your code. But you should look at the exact wording of the specific license in question to make sure that they explicitly state this and contact a lawyer if you are in doubt.