Sometimes Roman numerals are used to indicate the structure of a chord progression. The numeral I stands for the chord based upon the 1st note of the major scale (the key note). IV and V represent the chord taken from the 4th and 5th notes of the major scale, e.g., the following example is in the key of E, the 1st, 4th and 5th notes of the E major scale are E, A and B, therefore the I, IV and V chords are E, A and B. For simplicity, the numerals are indicated only on the basic progressions.
This example uses a different triplet variation than all previous triplet examples. Listen carefully to the recording to get the feel of this one.