Leitmotif
Also said as Theme, Motif, Character theme
A short tune tied to one character, place or idea, and brought back changed as the story goes. The same notes can be heroic in one key and broken in another.
It tells a story without words. A tune you learned in a happy scene, played slowly in a minor key, hurts more than any line of dialogue could.
Say it
“Write a seven-note motif for the sister. Play it on a music box when we meet her, on solo cello when she is lost, and on full brass in the last fight.”
Where you’ve seen it
Austin Wintory built Journey's score around a single theme, with a solo cello representing the player. It became the first game score nominated for a Grammy, in December 2012.
Not to be confused with main theme
A main theme is one piece for the whole game. A leitmotif is a building block that turns up inside many different pieces.