Page "Frigate" Paragraph 4

Frigates did not carry any guns ( or have any gunports ) on their lower decks ; confusingly, the lower deck was often referred to as the " gun deck " in the Royal Navy ( in the US Navy, it was usually called the " berth deck "), even for frigates, where it did not carry any guns or have gunports.

Both types could ( and usually did ) additionally carry smaller carriage-mounted guns on their quarter decks and forecastles ( the superstructures above the upper deck ).

Technically, rated ships with fewer than 28 guns could not be classed as frigates but as " post ships "; however, in common parlance most post ships were often described as " frigates ", the same casual misuse of the term being extended to smaller two-decked ships that were too small to stand in the line of battle.