Describe the bonding in a tribromide anion, what is its structure?
In fact, tribromide ion has the generic formula $\ce{AX2E3}$ according to Lewis diagram. Where  $\ce{A}$ is the central atom, $\ce{X}$ an atom bonded to $\ce{A}$ and $\ce{E}$ a lone pair on $\ce{A}$.  Using Valence Shell Electron Pair Repulsion (VSEPR) theory,  the geometry  of this ion will be
 :


So, the molecular shape is linear, while the electron pair geometry is trigonal  bipyramid.
 And the bonds in the ion are covalent.