Butch's girlfriend in Pulp Fiction, Fabienne, is quite significant. First of all, she shows the softer side of Butch. He's a tough boxer involved in some dangerous situations, but when he's with her, he's different. Also, she provides a contrast to the violent and unpredictable world of the other characters in the movie. Her character is more about love, loyalty, and a simple life. For instance, when Butch is on the run, he still thinks about getting back to her. So, she is like an anchor for Butch in the chaos of the movie's world.
Her significance is that she represents a normal life for Butch. She's his connection to a more peaceful existence outside of the criminal underworld.