Okay kiddo, so there was a time when two places in America, the East Coast and the West Coast, had a big disagreement about the music they liked. They both really enjoyed hip hop music, but they thought their own style of it was the best.
Some famous rappers from the East Coast were saying that their music was more about the lyrics and the story they told in their songs. These rappers were from places like New York City and Philadelphia. On the other hand, some famous rappers from the West Coast were saying that their music was more about the beat and how it made people want to dance. These rappers were from places like Los Angeles and San Francisco.
So, for a little while, these two groups of rappers did not like each other very much. They even started saying rude things about each other in their songs and making fun of each other. This is what we call the "rivalry" between the East Coast and the West Coast hip hop scenes.
Sadly, this rivalry got really serious and some rappers from both sides were hurt or killed. It was a sad time for hip hop music and it showed that we should never let disagreements turn into hate or violence. Now, hip hop music is enjoyed all over the world, and people from different places and backgrounds can make music together without fighting.