Black powder is a generic term these days, and it refers to propellants that were used in historical firearms, so those before the existence of cartridges. These are the muzzle-loading firearms, where the hunter, or the shooter in general, had to manually load the powder, which was a separate element of the loading process. Ordinarily it would be a small container commonly called a powder horn, where a measured amount of the propellant powder would be poured into the bore of the firearm and then the bullet would be manually seated. The ignition system would be primed and then the firearm could be fired.
Black powder is a very generic term referring in one sense to the original kind of propellant that was black in colour, which was a chemical combination of saltpetre, sulphur and charcoal. We're talking about a “days of the pirates” type of propellant powder. However, that term being generic now also refers to more modern formulations that don't involve the same chemical substances but which perform in a similar way. They're used almost exclusively in muzzle-loading firearms.