Product configuration enables companies to deliver customized products under the assumption that all the components and relationships between components are predefined. The premise that all the components and their relationships are predefined limits the effectiveness and accuracy of product configuration. In view of this, open configuration is proposed as an innovative concept to assist companies in configuring products that correspond exactly to what customer want. This paper provides the initial definition of open configuration. In the definition, open configuration involves three types of knowledge: predefined knowledge, dynamic knowledge and interaction knowledge. Predefined knowledge corresponds to predefined elements, while dynamic knowledge corresponds to newly defined elements; the interaction between them generates the interaction knowledge which contains modified components and interacted constraints. This paper uses a fridge configuration example to explain and demonstrate the procedure of open configuration. The result of this example shows that customer requirements which involve new elements can be fulfilled by open configuration.