Apps and Extensions on a Chromebook (or Chrome Browser), magnify the instructional and logistical functions of the Internet.
An App is essentially a stand alone web application that works within a SINGLE browser window. Some of these apps offer OFFLINE options so if you lose your Internet connection, you can still work.
Thanks to JR Ginex-Orinion for many of these.
An Extension adds some sort of functionality across all tabs and windows of your browser, usually by clicking on an icon at the top of the browser.
Google Docs Add-ons
Add-ons are a new feature found inside Google Docs and Spreadsheets.