Terminiology

Container

Container - the execution of an image
Image - a set of tarballs that contain the filesystem contents and run-time metadata of a container
Layer - one of the tarballs used in the composition of an image, often expressed as a filesystem delta from another layer

Ancestry - the Clair-internal representation of an Image
Feature - anything that when present in a filesystem could be an indication of a vulnerability (e.g. the presence of a file or an installed software package)
Feature Namespace (featurens) - a context around features and vulnerabilities (e.g. an operating system or a programming language)
Vulnerability Source (vulnsrc) - the component of Clair that tracks upstream vulnerability data and imports them into Clair's database
Vulnerability Metadata Source (vulnmdsrc) - the component of Clair that tracks upstream vulnerability metadata and associates them with vulnerabilities in Clair's database