So, back then before the bang of virtual theory happend people or organization used to run their application on buying a physical server in a particular data centre and those data centres needs too many equipment to manage their servers like network, temparature, hardware, security and lot of maintanance for it.
Suppose any organization bought 10 servers for and those each server comes with heavy configuration like 100's of CPU and 100's RAM and one of the organization runs their application on a one server which comes with this config and just using two of 100 CPU & two of 100 GB RAM and and left were remain unused that was very costly.
So, back then the concept came virtualization that is the solution of instead of buying 100's of server comes with those config simply using virtualization or virtual layer on a particular server and run one application for one server.
Suppose a organization in EUROPE or INDIA and My Organization need some servers for deploying my applications my employee will requesting the server anywhere from the world from the internet or cloud and they are giving me the server from the mentioned location and used it for deploying my application or website. This is the concept of cloud it has large network and it gives us remote servers around the globe so whenever we want the resources and we get it.
The cloud word refers to servers that are accessed over the Internet it is basically a hosted service used to store and manage data, running application and software over the internet and the physical data centre located in particular or several area around the globe, and it is maintained by the Cloud Provider.
Thank Yu !!