A melody makes the most direct appeal to the listener. It is what we remember, whistle and hum. 

It is a coherent succession of single pitches. We perceive the pitches of a melody in relation to each other, in the same way we hear the words of a sentence -- not singly but as an entire thought. 

Pitch: The highness or lowness of a tone, depending on the rate of vibration. The faster the vibration, the higher the pitch.

Interval: The distance between two different notes. Intervals may be large or small.

We describe the characteristics of a melody by its range, its shape and the way it moves.

Range: Melodies go up and down. The range is the distance between the melody's lowest and highest notes. The span can be narrow or wide.

Shape: Shape is determined by the direction a melody takes as it turns upward or downward or remains static. 

Movement: Conjunct and disjunct: A melody can move from pitch to pitch in small intervals, or it can move by leaps to more distant pitches. Melodies that move by small intervals in a joined, connected manner are conjunct. Those that move in disjointed or disconnected intervals are disjunct. Melodies do not necessarily remain the same throughout!   A melody may begin conjunct motion and become more disjunct.

The Structure of Melody

Just as a sentence can be divided into units or phrases, so can a melody. The phrase ends in a resting place, or cadence which punctuates a melody in the same way a period or comma punctuates a sentence.

The cadence may be inconclusive, leaving the listener with the impression that more is to come, or it may sound final.

Some music features simultaneous melodies called countermelodies.
 

Suggested Listening:

I. Overture to The Marriage of Figaro by Wolfgang Amadeus Mozart
Mostly conjunct movement, medium range

Mozart: The Marriage of Figaro (Highlights)

Karl Böhm, Conductor. Berlin Deutsche Oper Orchestra, Berlin Deutsche Oper Chorus
Deutsche Grammophon - #29822

The Marriage of Figaro: Complete

Herbert von Karajan, Conductor. Vienna Philharmonic.
Emi Classics - #67142

II. Mozart: Eine kleine Nachtmusik, third movement
Symmetrical phrasing
Mozart: Eine kleine Nachmusik, etc /...

Karl Böhm, Conductor. Vienna Philharmonic Orchestra
Deutsche Grammophon - #453076

III. Franz Joseph Haydn: Symphony No. 94 in G major, second movement
Countermelody begins about one minute into the piece.

Haydn: The London Symphonies Vol 2 /...

Sir Colin Davis, Conductor. Royal Concertgebouw Orchestra.
Philips - #42614