An origin is a package repository that contains both package metadata (such as catalogs, manifests, and search indexes) and package content (files). If multiple origins are configured for a given publisher in an image, the IPS client attempts to choose the best origin from which to retrieve package data.
A mirror is a package repository that contains only package content. Clients that install and update packages from a mirror repository must still download metadata from an origin repository. IPS clients access the origin to obtain a publisher's catalog, even when the clients download package content from a mirror. If a mirror is configured for a publisher, the IPS client prefers the mirror for package content retrieval. If multiple mirrors are configured for a given publisher in an image, the IPS client attempts to choose the best mirror from which to retrieve package content. If all mirrors are unreachable, do not have the required content, or are slower, the IPS client retrieves the content from an origin. See “Publishers and Repositories” in the pkg(5) man page for more information.