3 french hens

Today I have begun sketching out ideas for this year's Christmas card, which will be another in the black & white series based around one of the 12 days of Christmas. Previous cards in this series have been: 2 turtle doves, 5 gold rings, 6 geese a laying, and 7 swans a swimming. This year, I want to do '3 french hens'. I need to research exactly what french hen is!