Nessus is a scanner that primarily assesses the vulnerability of a network. In addition to checking for vulnerabilities, it can be expanded via plugins, templates, and policies to provide additional assessment capabilities, performing over 150,000 different checks.
The scope of the Nessus integration is currently limited to integrating compliance checks in SD Elements, specifically the CIS AWS Benchmarks Compliance checks.
A compliance check is a type of audit on a given system that checks to see whether that system is following security policies that are applied to it. SD Elements leverages the results from the Nessus AWS compliance checks to automatically mark the verification status of its security requirements.