What's the meaning of "string attached" ?

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:bust_in_silhouette: Asked By DriNeo
:warning: Old Version Published before Godot 3 was released.

In the home page we can read this.

" No strings attached, no royalties, nothing. "

I read this since a long time, but I never dared to ask this question.
Sorry for the noobish question, I’m not a native english speaker and not a professional developer too.

:bust_in_silhouette: Reply From: Zylann

As I understand it, “No strings attached” means that Godot is free to innovate, and it belongs to anyone given the MIT license. You can use it, contribute, modify it and make free or commercial games without the need to pay or have a contract with someone.

The term could refer to the way commercial engines restrict their usage to users owning a free version, or don’t offer source code access for example.