what is the difference between canonical and conjugate momentum.. ? what is its physical significant.. I was reading classical mechanics by Goldstein but could understood this terms
Exactly the same thing. You might use the term conjugate momentum when you're referring to the canonical momentum which is conjugate to a particular coordinate.
The canonical conjugate momentum p is derived via a derivative of the action w.r.t. the time derivative of a generalized coordinate q. Then {q,p}=1. The physical interpretation of p depends on the interpretation of q.