Cloud computing is a technology that allows users to access and use computer services and resources over the internet.
For example, instead of storing files on a physical hard drive, you can upload them to an online storage service like Google Drive or Dropbox. Similarly, instead of running software on your personal computer, you can use web-based applications like Google Docs or Microsoft Office 365.
Very Simple Definition:
Cloud computing is a way to use the internet to do things on a remote computer (a server).
For example, instead of saving pictures on your computer, you can save them on a website like Instagram. Similarly, instead of using a program on your computer to write a document, you can use a website like Google Docs.