"The cloud" in simple terms is any service or software that runs on the Internet as opposed to on your physical computer or device. Physical servers and storage located in data centres all over the world are accessible over the Internet, providing users subscribed to the service with the resources they require. By using cloud computing, users and companies do not have to manage physical servers themselves or run software applications on their own machines.
The cloud enables users to access files and applications from almost any device, because the computing and storage takes place on servers in a data centre, instead of locally on the user device. This is why a user can log in to their Instagram account on a new phone after their old phone breaks and still find their old account in place, with all their photos, videos, and conversation history. It works the same way with cloud email providers like Gmail or Microsoft Office 365, and with cloud storage providers like OneDrive, Dropbox or Google Drive.