What does it mean?
Well basically it allows other 3D programs to use Cycles for rendering.
Why do we care?
More people using it means more potential developer involvement, which means more features, and more artists to provide professional feedback.
What will change?
“Note that Blender Foundation and Blender Institute remain committed to further developing Cycles as a render engine for Blender. We welcome other developers to integrate it in other applications, and especially to get involved with the Cycles development team at blender.org.” –src
Cycles will still remain as it is now, be developed just the same by the Blender devs, and probably gain additional improvements anyone makes for it outside of Blender context.
Read the full story on the Development blog: