Trouble with cloud storage you never know who is peeking at your data, i run my own cloud via a WD nas drive a tad more secure,3tb and no monthly fee. As we have seen google etal seem to let the world and his wife snoop on your saved data
In this context a Cloud is simply a server, or a collection of servers that run 24 hours a day. You access them (normally) via the internet, and store data on them, as has been said by the others.
You can access your data via any computer, anywhere in the world, that is connected to the internet.
People who operate Cloud storage services go to some lengths to assure you that their system is reliable and secure, and that's where a question of personal judgment arises. You must decide whether or not you can have faith in these claims, and generally speaking you can; no Cloud service is going to survive for long if peoples' data security is compromised.