Office 365 E5 is a subscription-based plan offered by Microsoft that provides a comprehensive suite of productivity and collaboration tools for businesses. It is the most feature-rich version of the Office 365 suite and includes all the applications and services available in the lower-tiered plans, along with additional advanced features.

Some of the key features of Office 365 E5 include:

1. Advanced Security: Office 365 E5 includes advanced security features such as Advanced Threat Protection, which helps to protect against malicious attacks and phishing attempts, and Customer Lockbox, which provides customers with control over their data in the event of a service request.
2. Compliance Tools: With Office 365 E5, businesses can leverage compliance tools such as eDiscovery, which helps to identify, preserve, and collect electronic content in response to litigation or investigation, and Advanced Data Governance, which helps to manage data across Office 365 and other cloud applications.
3. Advanced Analytics: Office 365 E5 includes advanced analytics tools such as Power BI Pro, which provides interactive data visualizations and business intelligence insights, and MyAnalytics, which helps individuals track and manage their productivity.
4. Voice Capabilities: Office 365 E5 provides cloud-based voice capabilities through Skype for Business, which includes features such as PSTN conferencing, Cloud PBX, and Calling Plans.

Overall, Office 365 E5 is a comprehensive productivity and collaboration suite that provides businesses with advanced security, compliance, analytics, and voice capabilities, making it an ideal solution for larger organizations with complex IT requirements.