The term period furniture refers to pieces of furniture that are or were built in the style of an era that has already ended.
Especially in historicism (1850-1900), older furniture styles came back into fashion. Furniture from this period is not always pure in style, but sometimes mixes stylistic elements from different eras. With furniture from this period, for example, we speak of Empire style or Baroque style instead of Empire or Baroque.
Furniture in the antique style is still being copied today. If a deliberate attempt is made to copy an old piece of furniture, we speak of a forgery. If the actual date of manufacture is truthfully stated, we speak of full stop furniture.
In the photo you can see a Louis XVI style lady's desk. It bears typical classicist style features such as the festoon above the top or the fluting on the legs. Nevertheless, its later period of origin is clearly recognisable, e.g. by the traces of machining and the shape of the fittings.