A cough potion is presumably a potion which soothes and reduces coughing.
In 1996, Fred and George Weasley repackage their Love Potion as perfumes or cough potions so that they could be smuggled into Hogwarts, as Filch had put a ban on all Weasleys' Wizard Wheezes products the previous year.
See also
Appearances
- Harry Potter and the Half-Blood Prince (First mentioned)