Baby corn, as the name implies, are tiny, immature ears of corn. Both the kernels and the cob are soft enough to be eaten raw and they have a pleasing crunch and mild corn flavor. The ears are generally two to four inches long and about a half inch in diameter. They are most commonly used in Asian cuisine, especially stir fries, but are also found in salads and in salad bars. Interestingly, even though the United States is the largest producer of corn in the world it imports almost all of its baby corn from other countries. Thailand grows and sells the most baby corn, followed closely by Sri Lanka, Taiwan, and China. Most of this corn is canned or pickled in brine before shipping to improve shelf life.
Almost all varieties of corn can be picked prematurely, however there are also special varieties of corn that were bred specifically for producing baby corn. These cultivars were designed to produce ears of corn that are long and tapered and have neat, small kernels. Baby corn is generally harvested one to two days after “silking”, when the silk strands between the cob and husk begins to peek out the top of the husk. (For comparison, normal sized corn is harvested 20 to 50 days after silking.) It is critical to harvest baby corn within this two-day period. Waiting even a couple more days can mean that the corn has become too large and the cob too tough to eat. The husks must be picked by hand because the immature ears are so delicate.
Baby corn is most commonly found canned in most supermarkets in the canned vegetable or Asian cuisine sections. Higher quality baby corn can be found in glass jars instead of cans. Frozen baby corn is also available in some grocery stores. Some trendier restaurants and grocers in Europe and the United States have started carrying fresh baby corn, which apparently has a crisper crunch and a more natural corn flavor than the canned type. Fresh baby corn is often sold in its husk just like regular corn. It is normally eaten raw but can also be steamed and stir-fried and added to a variety of dishes.
http://oregonstate.edu/Dept/NWREC/babycorn.html
http://cru.cahe.wsu.edu/CEPublications/pnw0532/pnw0532.pdf