Patronage is simply a spot in office. "Patronage-hungry Jeffersonians" refers to Jeffersonians wanting/expecting a spot in office due to the change of political paties. (From Federalist to Republican) The significance is that Jefferson did not fire all the Federalists from their position to give the spot to Jeffersonians like expected. The people expected a drastic political change but instead, Jefferson made a subtle transition of power.
*(Smith said that the definition is short but that patronage is important because of the way it ties into Jefferson's subtle transition of power)*
Ask me tomorrow if you need further explanation -E.C.