3 H2O2 (aq) + KClO3 (aq) → KCl (aq) + 3 O2 (g) + 3 H2O (l)
This is an oxidation-reduction (redox) reaction:
ClV + 6 e- → Cl-I (reduction)
6 O-I - 6 e- → 6 O0 (oxidation)
KClO3 is an oxidizing agent, H2O2 is a reducing agent.
This is a gas evolution reaction, O2 is the formed gas.