The "Roll up Total ARR on Account across Closed Won Opportunities" field is a roll-up summary field that calculates the total Annual Recurring Revenue (ARR) associated with all the Closed Won Opportunities linked to an Account in Salesforce. It provides a consolidated view of the revenue generated from successful deals and allows for easy analysis and reporting at the Account level. This field helps sales teams and executives gain insights into the overall revenue performance and customer value for a given Account.