The label of a genus 2 curve over $\Q$ has the form $N$.$a$.$D$.$n$, where $N.a$ is the label of the isogeny class of the Jacobian of the curve (so $N$ is the conductor and $a$ is a string that distinguishes the isogeny class among those with the same conductor), $D$ is the absolute discriminant, and $n$ is a number that distinguishes the curve among other curves with the same absolute discriminant in the same isogeny class.