Your question cannot be answered directly. It's like saying "What's the difference between an apple and a Granny Smith?"
A CELTA IS
a TEFL, so it's difficult to say what the difference is. What one can say with some ease is that the CELTA is the Rolls-Royce of TEFLs. It is recognized internationally as the gold standard, to mix my metaphors.
Please see: http://www.tefl.net/tefl-courses/faq-te ... cation.htm
Hope this helps.