A melody is a sequence of notes (or pitches) that listeners hear as a single entity. Melody was a fundamental component of most Western classical music and much popular music, along with rhythm, harmony, timbre and dynamics, and it is usually the most memorable aspect of a piece.
Melodies can be ranked on a continuum from those that are the easiest to discern, such as nursery rhymes, to those which are very difficult or impossible to discern, as exemplified by much atonal music and especially serial music. A major trend in music composition in recent decades has been away from creating easily-recognizable and beautiful melodies and towards music with difficult-to-discern melodies or even no melodies. There is no single, clear explanation for this trend. It is often said to be a result of "all of the good melodies have already been used up," although there is no convincing evidence that this is true.
Another possible reason for this trend of downgrading or omitting melody is that it is much easier and faster for a composer to create a work that lacks a memorable melody than a work that has one or multiple easy-to-recognize and memorable melodies. It is no simple task to think up original, memorable melodies, as can be seen by the fact that throughout history very few people have been really proficient at it. Moreover, the truly effective use of melody can be much more difficult and time-consuming than merely creating a single, simple melody because it can also involve the complex process of melodic development, which includes creating well-positioned variations as well as contrasting melodies and counterpoint.