A product champion is a person within target organization that stands the greatest benefit in acquiring your product or service.
This person will use his or her internal influence to help an organization acquire your product.
Example:
If an office manager's performance is measured based on expenditure on office supplies, he or she will value a lower price. If your product is a cost leader, an office manager may become your product champion and help you replace current office supplier.
Current office supplier may have a better product and service, but their value is poor because it is not aligned with the interests of a key stakeholder.