Distributors vs. Wholesalers
A Distributor will sell and promote your books to the bookstores and libraries. They will have reps contact the stores and wholesalers who are most likely to want your book and pitch them the merits of your title.
A wholesaler has a warehouse and is a passive company that will purchase books from you, and then resell the books. They do not pitch your books, they wait and handle incoming orders only.
A distributor also has a warehouse. But they are not passive. They will store, pick, ship, invoice and collect on your behalf as well as handle customer service and most likely offer sales and marketing services as well. They are not your customer, they work for you. You give them money in exchange for the services they do for you.
A wholesaler is your customer. They buy books from you. Some of the bigger ones are called Ingram, Baker & Taylor, Bookazine, Brodart, New Leaf and Quality.
Ingram and Baker & Taylor are two of the largest book wholesalers in North America and they have warehouses all over the US. These warehouse hold book and when a retailer (bookstore or library) asks for a book, Ingram or B&T will send it to them. Both Ingram and Baker & Taylor offer distribution services as well, but only to a certain group of publishers and even though they have the word DISTRIBUTION in their names, they are most likely not distributing your books.
When a bookstore asks who your distributor is, you should be using names like NBN, IPG, New Shelves Distribution, Atlas Books or Book Hub. Ingram and B&T are not your distributor, but the bookstores will be happy to know that your book is available at those wholesalers.