The label of a genus 2 curve over $\Q$ has the form $N$.$s$.$D$.$n$, where

- $N$ is the conductor,
- $s$ is a string of letters that distinguishes this isogeny class among those with the same conductor,
- $D$ is the absolute discriminant, and
- $n$ is a positive integer that distinguishes the curve among other curves with the same absolute discriminant in the same isogeny class.

In particular, $N.s$ is the label of the isogeny class of the Jacobian of the curve. The values $s$ and $n$ are assigned as curves are added to the database and carry no intrinsic meaning