What is the 7 or 7th Scale Degree in music?

What is the 7 or 7th Scale Degree in music? The seventh scale degree is found 7 notes up a diatonic scale. This note is dissonant against the root of the scale. 

When added to a chord this dissonant tone adds an interesting sound to the chord. 

In the case of the Major 7 chord quality, listeners will perceive this chord as beautiful tonic landing place. 

Conversely, in the case of a Dominant 7th chord which uses a flat 7 interval.