What does the "cd" in "diltiazem cd" stand for? What does this drug do?

Controlled Delivery. Diltiazem is available in many different forms and has several brand and generic names. The “CD” following diltiazem stands for Controlled Delivery, which has an extended duration of action. For example, Diltiazem CD only needs to be taken once a day, while other formulations may need to be taken twice daily. Diltiazem can be used to treat high blood pressure and abnormal heart rates and rhythms.