Exchange Server is a mail server and calendaring server application developed by Microsoft.
Exchange is designed to centralise your emails into one database. Instead of your web-hosting company handling your email and them storing them on your computer, Exchange manages and backs up your emails on it’s server.
There are different levels of Office 365 packages that you can subscribe to, from email alone, or including all or elements of the Microsoft Office Apps (such as MS Word, MS Excel, and PowerPoint for example).