Elf-made wine is wine that is presumably brewed by house-elves.
In the summer of 1996, Severus Snape ordered his "assistant" Peter Pettigrew to bring a bottle so he (Snape) could serve it to sisters Bellatrix Lestrange and Narcissa Malfoy when they visited his home at Spinner's End in 1996. The bottle had probably been laying about for a while, as it was covered in dust. When poured out, the colour is revealed to be blood-red. They drank the first cups, toasting to the Dark Lord, and Snape had to force some more on Narcissa to calm her anxiety.
Later that year, Rubeus Hagrid and Horace Slughorn drank some wine as a way of respecting Aragog's death, with the latter testing all the wine with house-elves due to a bottle of mead tainted with poison earlier. Harry Potter refilled the bottles of wine with the Refilling Charm in order to get Horace drunk, making it easier to get a memory out of him.