Short answers, pulled from the story.
Melody is a linear succession of tones in the foreground of a musical work that the human ear perceives as a single coherent line rather than a random collection of sounds. It extends beyond simple frequency and duration to include tonal color and the emotional weight of silence between notes. The essence of a melody lies in its linear ordering rather than the specific instrument used to play it.
The music of the 1900s shattered conventions with a greater variety of pitch resources than had been the custom in any other historical period of Western music. Composers began to explore the full spectrum of available tones without the strictures of traditional harmony, and the chromatic scale became widely employed. This shift meant that a melody could be created from an unchanging set of pitches through dissonant dynamics alone.
The Norwegian composer Marcus Paus argued that many existing explanations of melody confine us to specific stylistic models rendering them too exclusive to capture the full scope of human musical expression. He claimed that the boundaries of what constitutes a melody are far wider than traditional theory allows. His perspective challenges the idea that melody is limited to fixed and easily discernible frequency patterns.
Different musical cultures utilize melody in ways that reflect their unique historical and social contexts creating a global tapestry of sound that defies a single definition. Jazz musicians use the term lead or head to refer to the main melody which serves as the starting point for improvisation. Indian classical music relies heavily on melody and rhythm and not so much on harmony as the music contains no chord changes.
Richard Wagner popularized the concept of a leitmotif which is a motif or melody associated with a certain idea person or place. This technique allows the music to carry narrative weight and psychological depth. The ability to recognize a melody across different contexts highlights the power of melody to connect the listener to the composer's intent and the historical moment in which the music was created.