Dilaudid (hydromorphone hydrochloride, "Drug Store Heroin") is an analgesic narcotic. It is a very potent painkiller (eight times as powerful as morphine on a per unit mass basis). Its addictive potential is similar to that of morphine.
Dilaudid is a prescription medicine, and can be administered orally, intravenously, or through a suppository. Its potency and prescriptive nature make it a common candidate for doctor shopping. Street prices are generally in the range of $50-$60 apiece, making it a rather expensive addiction.
Disclaimer: I would advise strongly against making any serious medical decisions (such as narcotics usage) based on unverified information made on any website. Dilaudid is quite potent, and can easily result in overdose if used carelessly.
"Dilaudid (Postponed)" is also a song by Velvet Acid Christ, and is the final track of Twisted Thought Generator. The title and lyrics, as is the case for many VAC songs, are likely influenced by the drug (perhaps literally).
Its tone is appropriately dark, yet mellow and soft.