melodic
Having a pleasant, easy-to-remember tune or musical sound.
Melodic means having a pleasant, flowing tune or melody. When you hear a song that's easy to hum along to, with notes that seem to flow naturally from one to the next, that's melodic music. Think of songs like “Somewhere Over the Rainbow” or “Happy Birthday”: the tune sticks in your mind because it's so melodic.
Melody is the main tune you sing or remember from a piece of music (as opposed to the harmony or rhythm). A melodic voice is one that rises and falls in a pleasant, musical way, like when someone's voice sounds almost like singing even when they're just talking. A bird's song might be described as melodic if it has a sweet, tuneful quality rather than harsh squawks.
Some music is intentionally not melodic: percussion music focuses on rhythm, and some modern composers create music that's more about interesting sounds than memorable tunes. But when music is melodic, it usually means you'll find yourself humming it later, sometimes without even realizing it.