A single source of truth (SSOT) is the practice of aggregating the data from many systems within an organization to a single location. A SSOT is not a system, tool, or strategy, but rather a state of being for a company’s data in that it can all be found via a single reference point.
A simple example of this is search engines. Let’s say a searcher enters a query about their favorite restaurant. Google aims to be the single source of truth for anything they may need to know about this restaurant; such as, the restaurant’s hours, phone number, local locations, menu link, ratings, and popular times. Google is bringing data from many sources (Google maps, the restaurant’s website, Yelp or Google ratings, etc.) to be the searcher’s single source of truth for the data they may want to know about that restaurant.