Windows Defender is a growing suite of protections from Microsoft. Some of these protections have changed names to join the Windows Defender family and that can be confusing.
Lenny Zeltser of security firm Minerva recently published this table to untangle Windows Defender protections and their dependencies.
As you can see the suite offers a depth of modern security protections. Priority touchpoints with PI System security best practices include:
Windows Defender Firewall with Advanced Security and Windows Defender Application Control (WDAC)
As of 31-Jul-2018, the Microsoft Enhanced Mitigation Toolkit (EMET) which we recommend for hardening PI Processbook environments has reached EoL.
Windows Defender Exploit Guard is the successor to EMET and is available on newer versions of Windows.