Virtualization is the core of cloud computing platform. In cloud we can create a virtual version of hardware, storage and operating system that can be used to deploy the application.
A cloud provider gives options to create virtual machines in cloud that can be used by its clients. These virtual machines are much cheaper than buying a few high end computing machines.
In cloud we can use multiple cheap virtual machines to implement a resilient software system that can be scaled very easily in quick time. Where as buying an actual high-end machine to scale the system is very costly and time taking.