Porter is a dark ale, brown to black in colour.
Compared to a stout, the alcohol level is lower, and the taste is lighter and slightly sweeter. Brown Porters tend be lighter than black ones.
A Porter uses dark-roasted malts, and is quite hoppy tasting.
Porters were historically were up to 7% alcohol by volume.
They were a combination of beers at first. Eventually around 1730, Harwood Breweries in London began brewing to match this combination on purpose.
Porter was advertised as more nourishing than other beers.
A stout at first was a “stout porter”, with “stout” having the meaning of “sturdy, strong”, as in a “strong porter.”