Office Online (previously Office Web Apps) is an online office suite offered by Microsoft as a part of Office 365, which allows users to create and edit files using lightweight, web browser-based versions of Microsoft Office applications: Word, Excel, PowerPoint and OneNote. The offering also includes Outlook, People, Calendar and OneDrive for Business, all of which are accessible from a unified app switcher (Outlook on the web).
Offline Data File (OST)
Typically, when you use a Microsoft Exchange Server account (Office 365 account), your email messages, calendar, and other items are delivered to and saved on the server. You can configure Outlook to keep a local copy of your items on your computer in an Outlook data file that is named an offline Outlook Data File (.ost). This allows you to use Cached Exchange Mode or to work offline when a connection to the Office 365 (Exchange) computer may not be possible or wanted. The .ost file is synchronized with the Office 365 (Exchange) computer when a connection is available.
OneDrive for Business
OneDrive for Business is Office 365's file hosting service. It allows users to upload and sync files to a cloud storage and then access them from a web browser or their local device.
OneNote is an electronic version of a paper notebook where you can write down notes, thoughts, ideas, scribbles, reminders, and all kinds of other information. Unlike the traditional document page format of other programs such as word-processing or spreadsheet programs, OneNote offers a free-form canvas where you can type, write, or draw notes in the form of text, graphics, and images wherever and however you want them.
OneNote Class Notebook
The OneNote Class Notebook is an Office 365 app that helps instructors set up OneNote in their class. This app will create a class notebook, which includes three types of sub-notebooks: Student Notebooks, Content Library, and Collaboration Space.
Microsoft's desktop email and calendar application. It is part of the Office suite and can be used to view email, calendar, contacts, and more.
Outlook 2016 for Mac
Microsoft Outlook 2016 for Mac is an email and calendar client that's available as part of Microsoft's Office suite. It is the latest version of Outlook for the Mac OS and can be used to manage email, calendar, contacts, and more.
Outlook Data File (PST)
A Personal Folders file (.pst) is an Outlook data file that stores your messages and other items on your computer. This is the most common file in which information in Outlook is saved by home users or in small organizations. Learn more.
Outlook on the web
Microsoft's service for accessing your Office 365 account via web browser. Log into Outlook on the web.
A profile is what Outlook desktop client uses to remember the e-mail accounts and the settings that tell Outlook which account(s) to connect to and where your e-mail is stored.