What does “BC break” mean?
Solution 1:
"BC break" usually means backward compatibility in a general term, but as David Schwartz said it can be interpreted as binary compatibility break in some contexts.
Solution 2:
A "BC break" is a binary compatibility break. Nokia documents it pretty well in the compatibility overview. Basically it means that code developed with earlier versions of a compiler, library, or operating system won't work on devices or run times built using a newer version.