• You are free to use Blender, for any purpose
• You are free to distribute Blender
• You can study how Blender works and change it
• You can distribute changed versions of Blender

In the last case you have the obligation to also publish the changed source code as GPL.

Anything you create with Blender - whether it's graphics, movies, scripts, exported 3d files or the .blend files themselves - is your sole property, and can be licensed or sold under any conditions you prefer.

Games created in Blender (.blend files) are program output and therefore not covered by the GPL. You can consider them your property, and license or sell them freely.
With stand-alone games however, any data that is included inside the actual stand-alone executable is covered by the GPL. If this is a problem then you should set up the stand-alone player so it reads from external .blend files. A common practice is to include a "please wait, loading..." scene in the standalone, and read level files externally.
The Blender standalone player or the game player can be sold commercially too, but you have to make it available under the GPL conditions.

In almost every circumstance for blender, only the code and other GPL'd files themselves are covered. Any output of such material is copyright the person who produced the output, in this case, the artist.

The splash-screen and icons are GPL'd material therefore when using them the terms of the GPL must be followed. Usage of the Blender Logo is only GPL too when used within the context of screenshots of the GUI with or without splashscreen.

The Blender logo is a trademark, usage guidelines are here.

The Blender Foundation logo is also a trademark, and only used for official Blender Foundation communications.

To enable documention (like books) with author copyrights, screenshots of GNU GPL applications are considered to be licensed as an author wishes. However, this only goes for the screenshot as a "whole", as an illustration of how the software works. Individual items in a screenshot (such as icons) are still GPL.

Copyright law in different countries actually differ in this area. Please consult legal advice if you're unsure.

The GPL allows for developers to work on Blender without worry that their work could be copied into a closed application. The GPL makes it so that all contributers must make their code open, this means that if someone distributes a version of Blender with a cool feature, everyone can have it.

One of the features of Blender is that it's truly "your own software". You or your studio can treat it as in-house software equally to the big powerhouses in the film industry.

OpenEXR is a project from Industrial Light and Magic, it is licensed under the a modified BSD license.  Same goes for the ZLib licensed Bullet Physics library, which is supported by Sony. BSD and Zlib license never require to publish changes in source code. Many firms contribute to some of the more advanced open-source graphics software.

The output of Blender, in the form or .blend files, is considered program output, and the sole copyright of the user. The .blend file format only stores data definitions.
In case you embed the .blend file with Python scripts, and the scripts provide bindings to other libraries or facilities, the next topic applies.

When a script uses calls that are part of the Blender Python Script Interpreter, the interpreted program, to Blender, is just data; you can run it any way you like, and there are no requirements about licensing that data to anyone.

The Blender Python Script Language is defined here:
www.blender.org/documentation/248PythonDoc/index.html

This only applies to the Blender Python API calls. Scripts still have to follow the licenses of other code, bindings or libraries that they might use.

If you link a Blender Python script to other libraries, plug-ins or programs, the GPL license defines they form a single program, and that the terms of the GPL must be followed for all components when this case gets distributed.

The bottom line is that we consider everything you can create in Blender as 'data', including Blender scripts. But when you extend Blender with "other facilities" you have to follow the regulations of the GPL.

OK is:
Author publishes a Blender script mixed with own code, under own license.

Not OK is:
Author publishes a Blender script, calling a compiled C library with own code, both under own license.

OK is:
Author publishes a Blender script, that calls other scripts with own code, under own license.

Not OK is:
Author publishes a Blender binary with own scripts, bundled under own license.

The divider is "If the script runs in the Blender Interpretor". When the script calls code not running in the Blender Interpretor you are making bindings to other facilities, and the regular GNU GPL rules apply.

Of course, you may give any of the versions of Blender on Blender.org to other people, or share it internally via a server. After 2.25 every version of blender can be freely distributed under the GPL.

Yes, but if you make modifications you must comply with the GPL and if they request the source code you have to distribute that to them as well. You can charge for the version of blender you give to your friends even, but it must be licensed under the GPL, and you may not charge an unreasonable fee for the source code.

The GNU GPL does allow your organization to use a modified version of Blender internally without offering the source-code as long as you do not distribute it outside your company or organization.