Yes, your mother's mother's brother is commonly referred to as your granduncle or great-uncle. This term denotes the brother of one of your grandparents. Alternatively, you could simply call him your uncle, although that is more commonly used for the brother of your parents.
That would be an uncle.
your uncle
Your Grand Uncle(great uncle) would be your grandmother or grandfathers brother.
uncle
Your mother's mother is your grandmother.
that would be your grand uncle
Your Grand-mother's brother - would be your great-uncle
Mothers brother ( uncle ) = amoo
Your relation to your mums uncle is GREAT uncle. You're welcome! 
He is your uncle, in most families he would be Uncle (Jack, Fred or what ever his first name is).
Grand Aunt or Grand Uncle depends what gender you are.
A Great half uncle.