Difference between "Mujiza" and "Karamat"

"M’ujiza" is the miracle, which is wrought at the hands of a Prophet and "Karaamat" is the miracle, which is expressed through the Saints .

If any apparent miracle is expressed through a non-Muslim and irreligious person, then it is called "Istidraaj."  As given in Sharh Aqaaid Nasafi, Pg. No. 144.

These miracles go against the accepted traditions/customs of the society and are seemingly impossible when judged the against the present corpus of human knowledge and are in fact an acknowledgement of the greatness of the Holy Prophet (Sallallahu alaihi wa sallam).  Thusi, Imam Nabhani (May Allah shower His mercy on him) mentions the opinion of Imam Shhabuddin Suharwardi in the foreword of his famous book, "Jame’ Karamat Ul Auliyaa":

Translation:  It is narrated on the authority of Imam Shihabuddin Suharwardi (May Allah shower His mercy on him), he says:  Indeed!  Various miracles are expressed through the Saints like they hear the divine voice (Hatif Ghaibi), they hear the voice of the inward (Batin) and recognize it, earth is rolled up for them and through the blessings of following the Holy Prophet (Sallallahu alaihi wa sallam), they know of incidents before they happen.  The miracles of the Saints are in fact the consummation of the miracles of the Prophets and are their blessings.  (Muqaddima Jame' Karamaat Ul Auliya, Pg. No. 36)