"Modulation" is a term in music, which indicates a change of key
within a certain passage. It is usually based on one chord which
becomes a type of "pivot chord", common to the first key as well as to the one to be attained.
In the musical example,we can see a Modulation from C major to F major. The third chord in this example is the "pivot chord", since it can be considered as IV in C major and I in the new key.
