TDU (or TDSP) charges are the portion of your bill attributed to your local utility, also called a Transmission and Distribution Utility.
The TDU is responsible for maintaining and repairing the power lines, poles, and infrastructure in your region, as well as facilitating the actual delivery of electricity to your home or business, regardless of which retail electricity provider (REP) you've chosen. These charges cover the costs of these services and are passed through to customers by REPs without markup. They can vary depending on the TDU that serves your area and are approved by the Public Utility Commission of Texas.
On your bill you might also see it line item using the specific TDU’s name. In Texas, the TDUs are Centerpoint Energy, Oncor, AEP, and Texas New Mexico Power.