Price books track the prices of products and services that your company offers to customers.
The standard price book is the master list of all your products and their default standard prices. Salesforce creates the standard price book when you start creating product records. It includes all your products and their standard prices regardless of any custom price books that include those products.
A custom price book is a separate list of products with custom prices, called list prices. Custom price books are ideal for offering products at different prices to different market segments, regions, or other subsets of your customers. Create a separate price book for each set of customers that you want to address. For example, if you have one set of prices for domestic customers and another for international customers, create a domestic price book and an international one.
Manage Price Books - https://help.salesforce.com/articleView?id=pricebooks_landing_page.htm