The name orzo comes from the Italian for little barley and this is another reason why some people think that it is not made from wheat. Originally orzo was made from barley but it is now always made from wheat. Barley too has gluten in it so this would still contain gluten even if it is made in the old fashioned way. Other people refer to it as Italian rice as it is Italian pasta but in the shape of rice and does contain just as much gluten as normal pasta.
Orzo is traditionally used in casseroles and soups as it has the texture of rice and pasta but is small enough to be eaten with a spoon without causing any mess.
Wheat always contains gluten and is the third most popular grain in the world. The two most popular are maize and rice. The reason why it is so popular is because it has a higher vegetable protein than maize and rice therefore works better as a carbohydrate as these carbohydrates cannot be broken down as well without any protein.
Other substitutes for pasta when on a gluten free diet are rice, potatoes, bread made from tapioca and rice flour and even some pasta, and this too is made from rice and tapioca flour.
As there are so many people who eat a gluten free diet, supermarkets are full of alternatives so have a look around and you are bound to find something that you can use in replacement for orzo.