The 4X Feliway Optimum Enhanced Calming Diffuser Refill is a lot of four 48 mL bottles of Feliway pheromone spray, specifically designed for cats. The refill bottles are for the Optimum model and have an expiration date of August 2026 or later. This product helps to calm and reduce stress in cats by providing them with pheromones that mimic the natural calming pheromones produced by cats. It is a convenient and effective way to create a peaceful environment for your feline companions.