A farm co-op is when one or more farms organize and sell "shares" of their produce and/or farm products to consumers directly. As a consumer, we buy one or more shares of the bounty and then throughout the year, we stop by the farm to collect our share of whatever is in season (usually weekly or bi-weekly). Shares can be determined however the co-op decides. Some use bags or boxes of produce. Some divide the crop evenly. So, if the co-op produces say 100 lbs of honey and has 10 shareholders, then each shareholder is entitled to 10 lbs of the farms' honey.
In theory, the farm and consumer both cut out the middleman which should make/save each group more money. This also gets seasonal produce into the hands of consumers quicker and spreads the risk of the farm's operation across multiple shareholders. Whether the farm has a great year and produces 1000 lbs of honey or a poor year and produces only 10 lbs. of honey, the cost to each shareholder is the same and the farm makes the same amount of money.
This is just the basics and each co-op has the latitude to operate as they see fit...
"We're just two lost souls swimming in a fish bowl -- year after year..."