The first time I heard this song was through headphones. I always loved Billie Holiday's voice, but to really experience her music, you have to watch her. Her facial expressions are so honest and heartfelt. You can tell that she deeply understands what she is singing about. She has seen it. The term "Strange Fruit" is a metaphor for lynchings. In the old south, when slaves became liberated, the white southerners became very angry when their "state's rights" to own human beings were made illegal. They began intimidation of the freed slaves. This is when the Ku Klux Klan became very powerful.
Billie Holliday was raised in Philadelphia, but her parents remembered life in the south. Billie was aware of the lynchings that took place in southern neighborhoods to blacks who simply said anything that could be taken as "dis-resepctful" to whites (as a Yankee in the south... I know how easy it is to accidently do this.) The song "Strange Fruit," and especially her magnificent performance, pushed northerners to "understand" how terrifying life still was in the post-Confederate south.