So sorry, obviously I don't get out enough.
GFCF--gluten and casein free, the proteins in wheat/barley/oats/rye and a few other less common grains, plus dairy proteins, cause problems for some of us (people react in many different ways to these, sometimes digestive, maybe rashes, maybe more neurlogical)... some of the non-GF grains (grains that do not contain gluten, I mean, that tend to be staples in a GFCF diet) are rice, buckwheat, corn and quinoa, but there are others
SCD--specific carbohydrate diet, is a very specific list of foods that tries to limit/eliminate one form of carbohydrate in order to reduce digestive stress and create a good environment for a healthy balance of gut bacteria--there are no grains, no dairy except for long-fermented yogurt, and a specific list of fruits and veggies and I think one or two legumes... it was apparently originally designed for celiacs working to heal the digestive damage done by their reaction to gluten, it's not also used a fair amount in the autism spectrum disorder community, moreso by kids who have significant digestive issues
GAPS--a very similar list of allowed foods as SCD, but the beginning of the diet is different, and it focuses more TF/Weston Price foods, homemade stock, fermented vegetables (gotta say homemade kimchee is really, really yummy), and it only adds in dairy carefully, but overall the idea is very similar to SCD
EFA--essential fatty acids, essential because we need to consume them via diet, we cannot make them in our bodies... the typical Western diet contains a low ratio of omega-3 fatty acids (DHA & EPA, the kinds that are plentiful in fish) vs omega-6 fatty acids (soybean oil, corn oil, most liquid oils have a lot more omega-6s, nuts and seeds are high in omega-6 as well, as are legumes like chickpeas, plus conventionally raised meat and eggs--but pastured meat and eggs have a much more balanced ratio--you can see why most diets are imbalanced toward too much omega-6).
One thing about EFAs, some people don't make one type of omega-6 well, GLA (gamma - something - acid) and so sometimes a supplement that includes that type of omega-6 is very helpful.