This is a rhythm pattern given to guitar students when they have advanced through several different 8th note strumming patterns.
This pattern basically consists of playing an 8th note, then a quarter note, and then repeating that pattern as much as possible. Repeating that pattern lasts 3 bars/measures. The 4th bar shown here is to keep with a standard 4 bars approach, and to throw in a quick break from the repeating pattern.
Here is the Guitar Pro 6 tab for this lesson:
John Taylor - guitar and bass instructor for Mile High Shred.