In general they are confused with the Stouts but there is a reason: the name Stout comes from a diminutive of the name "Stout Porter", used to classify the strongest Porters since Stout means "robust" or "strong" in English . Therefore, Porter is a milder beer than Stout would be. Overall a moderate strength brown ale with a moderate toasty and bitter character. It can have a variety of roasty flavors, usually without burnt qualities, and often has a chocolate, caramel, and malt profile. Aroma moderate to moderately low bready, malty with light roasting and may have hints of chocolate. It may also show some non-roasted malt character (caramel, nutty, caramel, and/or sweet). Medium-light to medium body, light to moderate creamy texture.
*Source: Beer Judge Certification Program (BJCP) - Beer Style Guidelines