The "tonic" is the first and central note of a scale. the principle of organization around a central note is called "tonality."
Tonic refers to the primary note of a scale that the scale depends on, sometimes called the root.
Most tunes begin and end with a similar tone which is the primary note, or tonic, in the scale. At that point you play notes from a scale you could hear that the music appears to float towards the main note, it resembles somewhere in the range of pressure is left until the point when you have achieved that first note. This phenomenon is called tonality.
