it means the main or mostly used part in a song or the main theme
It just means "melody". http://popularmusichistory.com/
I'm guessing you mean "unison."
Unison
Harmonize is a musical term referring to the way a chord and melody are used together. You can make harmony with chords accompanied by melodies when created musical pieces.
In a vocal solo, the voice is the melody.
Melody is the principle part of any tune, or air.
longated
Quasi is an Italian musical term meaning: As if, resembling
The word "fugue" is usually used as a musical term. It refers to a piece of music which consists of two or more parts, each with a similar melody. Bach was noted for his fugue compositions.
Musical instrument(s). The word has its origin in the Hebrew "klei zemer," instruments of melody.
The "A" melody
A melody is a succession of musical notes, played in sequence. A chord is a collection of musical notes all played at the same time.