Microsoft Office 365 for professionals and small businesses is a subscription service that combines the familiar Microsoft Office Web Apps with a set of web-enabled tools that are easy to learn and use, that work with your existing hardware, and that come backed by the robust security, reliability, and control you need to run your business.
Email & calendar
Office Web Apps
Websites & collaboration
IM & online meetings
Office 365 is designed to deliver reliability, availability, and performance with a guaranteed 99.9% uptime, financially backed service level agreement (SLA).
Note: All the information is taken from the official Microsoft website.