Modern furniture refers to furniture

Furniture

Furniture is the mass noun for the movable objects intended to support various human activities such as seating and sleeping in beds, to hold objects at a convenient height for work using horizontal surfaces above the ground, or to store things...

 produced from the late 19th century through the present that is influenced by modernism

Modernism

Modernism, in its broadest definition, is modern thought, character, or practice. More specifically, the term describes the modernist movement, its set of cultural tendencies and array of associated cultural movements, originally arising from wide-scale and far-reaching changes to Western society...

. It was a tremendous departure from all furniture design that had gone before it. Dark or gilded carved wood and richly patterned fabrics gave way to the glittering simplicity and geometry of polished metal. The forms of furniture evolved from visually heavy to visually light.
Prior to the modernist design movement there was an emphasis on furniture as ornament, the length of time a piece took to create was often a measure of its value and desirability.