Mead is an alcoholic beverage made by fermenting honey that has been diluted by water. Mead was popularised in classical Greece and imperial Rome. It became the favourite drink of many European tribes after the fall of Rome. Mead is also a favourite drink in the Wizarding world.
Harry first had Mead in the summer of 1996 when Dumbledore arrived at 4 Privet Drive to explain Sirius Black's will to him. He remarked that though he had never had anything like it, he enjoyed it immensely.
In Harry's sixth year at Hogwarts, Professor Horace Slughorn gave Ron Weasley a glass of oak-matured mead, after giving him the antidote to a Love Potion as a pick-me-up, unaware that the mead had been poisoned by Draco Malfoy via a bewitched Rosmerta, who had intended that the mead bottle reach Dumbledore; Argus Filch did not detect the poison due to him not recognising poison, nor did he doubt anything from Rosmerta. Only quick work by Harry Potter, who shoved a Bezoar down Ron's throat, saved his life. Dumbledore would later comment to Draco that this was a crude and desperate method of assassination.