A Dominant Seventh chord, also known as simply a 7th Chord, has a major triad plus a minor seventh interval.

 

For instance, C7 chord has the notes C, E, G, Bb, an A7 chord has the notes A, C#, E, G, and so on.  

 

The Swars are Sa, Ga, Pa and Ni.

 

Another way of understanding a 7th chord is to see it as a combination of two overlapping triads. A 7th chord has a major triad and a diminished triad overlapping each other. A C7 chord has the notes C, E, G, Bb. So, if you take the first 3 notes you get a C chord and if you take the last three notes, you get an Edim chord. 

 

Dominant 7th chords are very common in Bollywood songs and are used in different ways to enrich the music.  The most common use is to play a 7th on the 5th interval of the scale or the Pa Swar. For instance, if you are playing in the key of C Major, you can probably cover the entire song with C, F and G chords. Now try substituting the G chord with a G7 chord, it will sound great, especially when moving from a G7 to a C chord.