I got asked this question after my last CSA post. In case anyone else is wondering, here is the answer.
CSA stands for Community Supported Agriculture. In a nutshell, when you sign up for a CSA share, you are basically subscribing to a farm and promising to buy a certain amount of produce from them. This gives the farmer cash upfront that they can use to grow the food instead of waiting for it to go to market where it may or may not be sold. In exchange, you receive your share of what the farmer grows. In the most basic model you share in the risks and rewards of farming. If the farm you are subscribed to has a great harvest, you could end up with pounds and pounds of beautiful fruits and vegetables to gobble up, can, freeze, dehydrate, give to friends and neighbors, bribe politicians with, etc. If there is too much or too little rain, it freezes, locusts swarm, or the aliens get carried away with crop circles, you could end up with a rather sad looking basket that week. Many farms, such as the one I am subscribed to, minimize your risk by supplementing their produce with other local farms. So while I am never going to get enough strawberries to make jam, I get a greater variety of fruits and vegetables each week than would be possible if my farmer had to grow everything himself. Often the farm will have events for their subscribers, and some give you the opportunity to help out and do a little farming yourself.
Generally you sign up for a certain number of weeks. Where I live the farmers can grow year-round, so I sign up by the quarter. In other parts of the country you might sign up for the growing season. Sometimes you have to go to the farm to get your share, sometimes they have various pick-up locations or bring it to the farmers market. Some CSAs even deliver to your house. I belong to the South Coast Farms CSA, so I pick up at their farm in San Juan Capistrano because Beck likes visiting and sitting on the old tractors they have out front and checking on the chickens. They also have pickup locations throughout Orange County.
To learn more and find a CSA near you, visit one or more of the following websites, do a Google search for Community Supported Agriculture in your area, or ask around at your local farmers market.