What is the difference between Standard and Custom Price Books, and how does multi-currency affect them?

A Standard Price Book is the system default and contains the list price for every active product. Every product must have an entry in the standard price book before it can be added to a custom price book. A Custom Price Book contains a subset of products at negotiated or market-specific prices and is associated with an opportunity or quote to drive pricing. Typical use cases: regional pricing, partner pricing, or segment-specific discounts. With Multi-Currency enabled, each price book entry can have a price per active currency, and Salesforce converts amounts to the corporate currency using the defined exchange rates. With Advanced Currency Management (dated exchange rates), currency conversion on Opportunity Amount and related fields uses the exchange rate in effect on the Opportunity Close Date rather than the current rate, providing historically accurate revenue reporting.