A female character with well defined muscles. Use the tag only when there's visible muscles in any of the areas such as arm muscles, shoulder muscles, thighs, etc. not just the abs. An athletic physique does not mean a muscular physique.
Please refrain from using the tag for comically muscular or completely masculine characters who are drawn intentionally to look like men such as Oogami Sakura or the true form of Biscuit Krueger (as seen in #3652484).