A guitars "action" is the heigth of the strings from the fingerboard. Guitars with low action play easier, but when when the strings vibrate against the frets they cause "fret Buzz" or "fret out". This causes a thinning of your tone. As little as a 1/4 turn counterclockwise at the bridge can held elivate minor buzzing. Truss rod adjustments can also eliminate buzz on both acoustics and electrics, but please consult a professional guitar repairman and make minor adjustments and live with them a couple of days. There are several books on guitar repair that make it easy to understand and measure truss rod adjustments.
Here is a video on truss rod adjustment by guitar repair guru John Carruthers...