七草 or Nanakusa means "seven herbs." In Japan, there is a custom to eat nanakusa-gayu (seven herb rice gruel) on January 7th. These seven herbs are called "haru no nanakusa (seven herbs of spring)." It is said that these herbs will remove evil from the body and prevent illness. Also, people tend to eat and drink too much on New Year's Day, therefore it is a ideal light and healthy meal with a lot of vitamins. There are also "aki no nanakusa (seven herbs of autumn)," but they are usually not eaten, and used for decorations to celebrate the autumn equinox week or the full moon in September. (Thanks to About Japanese for the above.)
Here are the herbs in question...
春の七草 (Haru no nanakusa): Seri (Japanese parsley), Nazuna (shepherd's purse), Gogyou, Hakobera (chickweed), Hotokenoza, Suzuna, Suzushiro
秋の七草 (Aki no nanakusa): Hagi (bush clover), Kikyou (Chinese bellflower), Ominaeshi, Fujibakama, Nadeshiko (pink), Obana (Japanese pampas grass), Kuzu (arrowroot)
I didn't eat any of the above today, but I did sprinkle some celery salt on my pizza...does that count?