Performance Max(PMax) is Google’s new way to streamline and simplify advertising across its platforms. The new system is a goal-based campaign type that helps link you to customers across YouTube, Display, Search, Discover, Gmail, and Maps.
Performance Max (Pmax) is a campaign type that provides a unified buying service to all Google Ads inventory. Instead of setting up separate campaigns for YouTube, Display, Search etc., you set up only one campaign which targets all of these platforms. It helps advertisers optimize performance, in part by reducing the complexity and overhead needed to manage multiple campaign types.
Performance Max Retail refers to Google Shopping ads related campaigns.