Come in, she said

CSA stands for "Community SUpported Agriculture". The shares are essentially people in the community pre-paying for their vegetables (buying a share in the summer's crop) and then getting a box of veggies every week for the summer. Farms get money up front, at the start of the growing season, before they have produce to sell, buyers usually get a better price on produce (at least in a good harvest year) than they would at the farmer's market.