An eosinophil is a cell! More specifically it is a white blood cell, and even more specifically it is a white blood cell of the immune system. It is responsible for inflammation, which is a good thing when it comes to fighting off infection etc. A very bad thing when it comes to fighting food. Eosinophils working properly help fight off bad things. When not working properly they can cause permanent pathological changes in your body.
Here is a picture since the human eye cannot see it.

How do you say it? eee-oh-sin-oh-Phil (I like my version better than Google's)
What is an EGID? EGID is stupid for Eosinophilic Gastrointestinal Disease. Basically an abnormal amount of this white blood cell, in a specific area of the digestive system. Why is this disorder so crucial in children? It can cause so much damage and inflammation to the GI system that digestion of foods and absorption of nutrients is impossible. Malnutrition in children is linked to Developmental disabilities, organ failure and ultimately death. Simply put, when the body cannot absorb proper nutrients, bad things can happen.
So, is this a death scentance? Absolutely not!
Is there light at the end of the tunnel for people that have this condition? Absolutely!
Is it hard to completely adjust your life? Absolutely!
Is it imposible? Absolutely not!