In this paper we propose a novel workflow definition language - called the CLWfDL (Cloud Collaboration Workflow Definition Language) - for defining workflow in the working model of cloud collaboration. The language enables the distributed definition and concurrent revision of a workflow by multiple users from different places in the cloud. Users who participate in defining a workflow can use the language to specify their own requirements for the workflow execution. Each user can selectively contribute to part of the workflow definition. Any conflicts between the requirements of different users can be detected automatically. A single flow-control construct such as AND-join or OR-split can incorporate the requirements of multiple users. We have also implemented a translator of the proposed language that can translate the requirements collected from multiple users into other workflow definition languages.