It's a fairly common informal way of writing the chemical formula (H2O2) that tries to be a little more faithful to the geometry of the molecule... so HOOOH is

It's a fairly common informal way of writing the chemical formula (H2O2) that tries to be a little more faithful to the geometry of the molecule... so HOOOH is hydrogen perperoxide, literally a chain of three oxygen atoms with a hydrogen atom at either end. In my electrochem (Chem 2) class, the instructor used to sometimes write HOH for water.