What the difference between deadlock avoidance and deadlock prevention?

I met two terms and are they the same thing or different thing?

From stackoverflow

• You could look at it as:
  Avoid: Don't share resources across processes / mulitple threads
  Prevent: When accsessing shared resources, use a semaphore.

• Wikipedia is your friend.

  • http://en.wikipedia.org/wiki/Deadlock#Prevention
  • http://en.wikipedia.org/wiki/Deadlock#Avoidance