A triad is a 3-note chord of some kind, and an augmented triad is composed of a major 3rd stacked on top of a major third. That creates the “unbalanced” sound typical of an augmented triad. This short video demonstrates how a major triad can be turned into an augmented triad with just one change:

For more information on augmented triads and a free cheat-sheet, come over to Augmented Triads