Dark, CSA stands for Community Supported Agriculture.
It's a way for the food buying public to create a relationship with a farm and to receive a weekly basket of produce. By making a financial commitment to a farm, people become "members" (or "shareholders," or "subscribers") of the CSA. Most CSA farmers prefer that members pay for the season up-front, but some farmers will accept weekly or monthly payments.
(from this website
They work various ways, but basically you get fresh seasonal fruits and veggies, similar to those you'd buy at a farmers' market, that is local and perhaps organic. But, you get them regularly, and for the most part you don't get to choose what you get. The one I belong to tells me a few days ahead what they're sending, and I can substitute up to 5 items either by doubling up on something else or choosing a substitute from a list. It's a great way to try new things, and the price - at least for me - is no more than buying mediocre produce at the grocery.