Previously, server based BizTalk adapter was used to access MQ Series and that requires MQ series server on Windows as intermediate server between BizTalk Server and non-Windows Queue Managers. In some situation, when installing the MQAgent to Windows MQ Series box is not an option the client based BizTalk adapter (MQSC) is needed to achieve the same goal.
Go and have a read here: BizTalk MQSC Adapter