Zero. As in zero points, zero games, or zero sets. The origin is debated, with the most popular theory being that it comes from the French word 'l'oeuf' (egg), because an egg looks like a zero. Whether or not that's actually true, it's stuck. '6-love, 6-love' is the most brutal possible scoreline in a two-set match.
"Love-thirty. She hasn't won a point on serve this game."