A flamenco guitar is a Spanish or classic guitar with certain nuances that make its timbre or touch different.

Types of woods

The different choice of woods for flamenco or classic guitars was greater long ago, since different woods were used for these two styles.
Today instrumentalists may choose different timbres, because of this the type of wood is not a defining element anymore.

Guitar size

The size is a defining element today, since the sound board in a flamenco guitar is smaller and the sides are not so wide.
This is due to the fact that a flamenco guitarist needs the sound to come out with strength and vanish quickly.
The guitar scale, the distance between the nut and the saddle, is not so different today, since the guitarist will choose one of another on the basis of comfort and taste. The most usual scales are 650 mm, 660 mm and 670 mm.

Fret buzz

The sound in a flamenco guitar is not so clean and clear as in a classic guitar, due to the fact that in a flamenco guitar the strings are closer to the fingerboard and this sometimes produces fret buzz on strings five and four.
This will also depend on the guitarist’s strength when he plays. Strings 1, 2, 3 usually produce a high-pitched sound that stands out when the guitarist makes a “rasgueo”.
When we talk about string action, we refer to string height, that’s to say the distance between the string and fret 12 and the string and the bridge area.

My experience

In my experience as a guitarist I have played guitars with very different string actions, guitars with a 9 mm height between the strings and the bridge and 2,5 mm height in fret 12 that I found really comfortable; as well guitars with 8 mm height on the bridge and 3,5 mm height on fret 12 that were really uncomfortable because of the neck width. 
This also plays an important role, anyway every guitarrist is different and has different preferences. In a flamenco guitar the usually height ranges between 2,5 and 3,2 milimetres on fret 12 and between 7 and 10 mm on the bridge