Gray asexuality is when someone experiences little to no sexual attraction, but occasionally they might experience some form of attraction. Imagine a food you don't really like, but sometimes you might still want to eat it if you're really hungry or if it's the only thing available.
Similarly, gray asexual people might not feel sexually attracted to anyone typically, but sometimes they might feel a slight pull towards someone, but even then it might not be strong or happen often.
It's like different shades of a color: you're still on the asexuality spectrum, but you might not fit into the "black and white" labels of completely asexual or sexual. Just like how a light gray color isn't completely white, but it's not completely black either - it falls somewhere in between.