What is "hungarian gypsy scale"

Hungarian scale or Hungarian Gypsy Scale is a name given by different authorities to two different scale forms.

The more commonly used of these scales, also called Hungarian minor scale or double harmonic minor scale, can be found by sharpening the 4th degree of the harmonic minor scale to introduce an additional gap, or augmented second. This is a symmetrical scale that is very common in Flamenco. In Indian classical Carnatic music, it is known as the ragam Simhendramadhyamam. It also shows up occasionally in Western Classical music selections, such as mm. 5-6 of Liszt's Sonata in B Minor. The scale is often used in the 5th mode, in which case it is referred to as the double harmonic scale.

The alternative (and less common) version is the asymmetric Aeolian 4 scale, the only difference being that the 7th degree of the scale is not raised. This form of the scale can also be used in the 5th mode and would then be referred to as the Neapolitan scale.