Well if you go to cooking school the term means a mixture of beaten eggs and some sort of liquid which is then brushed onto foods prior to baking.
When you brush the egg wash and it adds a golden color and sheen to the baked goods.
Also when baking it is also used as a glue to secure two edges of pastry together like when you make filled pastries. It can also be used for calzones, won tons, the list goes on.
Egg Wash Recipe: The typical egg wash recipe consists of about two tablespoons of liquid for each egg. Using less liquid creates a darker egg wash. Egg wash is usually made with water, although milk can be used, too. Some egg wash recipes call for a pinch or so of salt as well.
When you apply your egg wash make sure you do not apple it to heavy/thick. It may seep down in between your crust and the pie pan and it may seal them together. Also if it is to thick it won't seal it will just be a mushy mess.
