What is the name of Al(OH)_3?

The name of $\text{Al(OH)"_3}$ is aluminum hydroxide.
Ionic compounds are named for the elements or polyatomic ions of which they are made. We can know this is an ionic compound because it contains a metal ion and a polyatomic ion. The metal ion is $\text{Al"^(3+)}$ and the polyatomic ion is $\text{OH"^-}$, called the hydroxide ion.