Essential fatty acids are fatty acids that are required by the body but that cannot be manufactured by the body (and therefore must be consumed).
There are two known essential fatty acids, or EFAs: linolenic and linoleic acid. These acids are the "parent" acids of omega-3 and omega-6 because the body can transform these EFAs into those fatty acids.
How much you should have: About 20 to 50 mg of ALA acid per day is standard, though more may be taken if desired. Linoleic acid should limited to about 7 mg per day, about the amount in one tablespoon of soybean oil.