Product data: Product name, price, category
Marketing campaign information: Traffic source, medium
Transaction data: Cart value, checkout date
Customer information: New or returning customer
Data layer variables enable Tag Manager to read values from your data layer implementation and pass those values to tags, triggers, and other variables. A data layer object is made up of a list of key/value pairs. A key is a category of things – a book's category, title, or author. Each key could have different values. A book's title key could have a value of 'Ulysses', 'War and Peace', 'A Brief History of Time', etc.