Computing today is covered with Clouds, remote storage opportunities. You store something in "the cloud" and you don't know where it is. That doesn't matter because some sort of software can find it when you want it. When you buy Kindle books from Amazon, you don't have to have an e-copy of every book on your device because Amazon keeps an "archive" of your books for you. You can contact the archive with the Kindle reader or other device and retrieve a copy when you want it. Your archive is in the cloud.
If you use Google Drive or Docs, you can create word processing, spreadsheet and other types of files on your computer or tablet but your work gets saved in the cloud. You don't know where your creation is but it is on a computer ('server') somewhere in California or Kansas or Costa Rica or some place. One of the reasons to use such an arrangement is that you can access the cloud from anywhere and normally from any computer. You don't have to carry your portable, backup drive with you or remember it to be able to access your files.
Many of the large computing-related businesses offer cloud storage these days. It helps the business if you have their name and cloud access method in mind each time you want to retrieve one of your files. There may be an opportunity to place an ad here or there on the way to the file that you want. Ads need to be paid for and bring in revenue. In addition to the cloud storage of Google's Drive and Apple's iCloud and such, there are separate storage businesses such as Dropbox and JustCloud. Many teachers and students like Dropbox, which may have special features for special uses, such as checking any file submitted by a student to see if it matches some other document on the internet and it thus an example of plagiarism instead of original work.
Cloud services need to be able to function with a variety of file formats and generally can do so. You might not want to place highly sensitive information in the cloud since you can't be sure who or what else might have access to it.
Flash (a.k.a. thumb) drives work as small, portable external storage devices that store files for later retrieval. Some thumb drives nowadays have the ability to accept files for storage using the local wi-fi system in your house or business or the coffee shop or hotel. In a sense, such ability makes the device a micro-cloud but it may need to physically near your signal source or the device sending the file. Very short-range transmissions of that sort often use the format and method called "Bluetooth", as in many of today's cars.
