What makes a chord augmented?

The fifth note of the triad is raised one step, e.g. the augmented c major chord, instead of being C E G, would be C E G sharp.

an augmented triad is made up of two major thirds stacked ontop of eachother. in other words, if you started on a C, your chord would be C, E, G#

Rose has it exact - two major thirds stacked create the triad - (example: C E G#).

Appearing in any order, notes with these intervals are augmented.

To further add to the other answers, augmented in musical terms means to be bigger. The intervals in an augmented chord are bigger, just as those in a diminished chord are smaller (than a triad) - a diminished chord has 2 minor thirds (away from your tonic, then a minor third from that) wheras an augmented has 2 major thirds.

Two major thirds on top of each other, as opposed to the usual major third over a minor third. diminished is the opposite: two minor thirds, one over the other.

the intervals 1,3,5 is a triad, but if you rais the fifth it would be 1,3,#5, which makes it augmented. you can do this with 7th chords also not just triads.

chords that are broken up. i think.