"cinnamon bun" are largely interchangeable, and  both refer to a sweet, spiral-shaped pastry that's  

made with a yeasted dough, filled with cinnamon  sugar, and typically topped with a glaze or icing.

In some regions, there may be slight  variations associated with these terms.  

Some people might use "cinnamon roll" to  describe a simpler, more bread-like pastry,  

and "cinnamon bun" to describe a richer,  potentially more buttery and sweet version.

This distinction, however, is not  universally recognized and largely  

depends on regional dialects  and personal preferences.

Another potential distinction could be the shape,  

with "rolls" often being more tightly  wound spirals, and "buns" being a bit  

looser and potentially larger. Again, this  isn't a strict rule and varies widely.

In summary, there isn't a significant difference  between the two, and you can generally expect  

the same type of pastry regardless of whether  it's called a cinnamon roll or a cinnamon bun.