A large book of maps. People buy it to figure out the interstate highways. Contains the "big picture" useful if you are hopping from city to city. The name has the word "atlas" because you can often see an entire state or country illustrated within two facing pages. But the little things this book omits matters a great deal too. For example, the book can't tell you which local restaurant is great or not. Something like the Michelin Guides will help you with that.
Once you settle down in a city though you'll want a book that maps the entire city's roads small and large. Such a book would be much more useful for day to day use than a road atlas.
A road atlas cost a little more than a Happy Meal.