From the article "Five9 is a pioneer of cloud-based contact center software. Its highly-scalable and secure cloud contact center delivers a comprehensive suite

From the article "Five9 is a pioneer of cloud-based contact center software. Its highly-scalable and secure cloud contact center delivers a comprehensive suite of easy-to-use applications that allows management and optimization of customer interactions across many different channels". In less corporate speak , as someone mentioned it's a call centre management solution.