Br2 (aq) + 2 KClO3 (aq) → Cl2 (g) + 2 KBrO3 (aq)
This is an oxidation-reduction (redox) reaction:
2 Br0 - 10 e- → 2 BrV (oxidation)
2 ClV + 10 e- → 2 Cl0 (reduction)
Br2 is a reducing agent, KClO3 is an oxidizing agent.
This is a gas evolution reaction, Cl2 is the formed gas.