The Gluten-Free diet is simply a diet without gluten. Gluten is most commonly found in wheat but is also found in the seeds of wheatgrass and barley grass, but not in the actual grass. Cross-contamination is a big concern for people who are gluten-free. If a package has been certified gluten-free then it is made in a facility that doesn’t have gluten in it, if not then there is a small chance of contamination. Most people who avoid gluten either have celiac disease, which is where your body reacts badly to gluten and it can make you feel really ill, or a gluten sensitivity which isn’t as severe but is still a reaction to gluten.
Read more on Celiac.org