Does Light Ever Travel Faster or Slower Than Speed C?

[journeytospace]

I read from 'strange theory of light and matter' by feynman that light also travels faster and slower than C but on an average it travels at C..can anyone explain the reason behind or give me some links..

 

[Gauged]

I suggest that you reread which ever passage that you're alluding to, or perphaps copy, word for word, the exerpt, so that it may be explained to you in other words.