The ScmKey field in the Issue table is a bigint data type, which is typically used to store very large integer numbers. This field is commonly associated with source code management (SCM) systems, which are used to track changes made to software code throughout the development process. In this context, the ScmKey may be used to uniquely identify a specific version or revision of a code base. This field can be used for referencing, tracking and organizing code changes within the Issue table, making it a valuable tool for developers and project managers alike.