H2S is oxidised to S.
H2S is the reducing agent.
Cl2 is reduced to HCl.
Cl2 is the oxidising agent.
So it's a redox reaction
An oxidation-reduction (redox) reaction is a type of chemical reaction that involves a transfer of electrons between two species. An oxidation-reduction reaction is any chemical reaction in which the oxidation number of a molecule, atom, or ion changes by gaining or losing an electron.