* Compound: A substance formed when two or more different elements are chemically bonded together in a fixed ratio. Hydrobromic acid (HBr) is formed by the chemical bonding of hydrogen (H) and bromine (Br) atoms.

* Element: A pure substance that cannot be broken down into simpler substances by chemical means. Hydrogen and bromine are elements.

* Homogeneous Mixture: A mixture where the components are evenly distributed throughout the mixture and have a uniform composition. While a solution of hydrobromic acid in water would be a homogeneous mixture, hydrobromic acid itself is a pure compound.

In summary: Hydrobromic acid (HBr) is a compound because it's formed by the chemical combination of two different elements (hydrogen and bromine) in a fixed ratio.