ISP stands for Internal Service Provider. ISP is a UVA department/unit providing goods or services to internal customers such as faculty, staff, students, and other departments.
ISD stands for Internal Service Delivery. ISD is a Workday transaction that records critical information related to the item(s) that an ISP provides to a requester. When approved, it generates revenue/recovery for the ISP and expense for the requester.
In other words, an Internal Service Provider (ISP) uses the Create Internal Service Delivery (ISD) task to charge the internal customer's FDM worktags.