Plastic arts are art forms which involve physical manipulation of a plastic medium by moulding or modeling such as sculpture or ceramics. The term has also been applied more broadly to all the visual arts (such as painting, sculpture, film and photography).
Materials for use in the plastic arts, in the narrower definition, include those that can be carved or shaped, such as stone or wood, concrete, or metal. The term "plastics" has been used to mean certain synthetic organic resins ever since they were invented, but the term "plastic arts" long preceded them. The term should not be confused, either, with Piet Mondrian's concept of "Neoplasticism".
1 : art (as sculpture or bas-relief) characterized by modeling : three-dimensional art
2 : visual art (as painting, sculpture, photography or film) especially as distinguished from art that is written (as poetry or music) --often used in plural
Therefore, it is safe to say that plastic arts in the narrower sense are those visual arts that involve the use of materials such as clay, plaster, wood, gold, silver or copper, for instance, that can be moulded or modulated in some way, often in three dimensions.
In contrast to the limiting of 'plastic arts' to sculpture and architecture by Friedrich Wilhelm Joseph Schelling in 1807, the German critic August Wilhelm Schlegel (1767-1845) applied the concept not only to visual arts, but also poetry. Classical poetry lines he saw utilising plastic isolation, and rhyme falling under the Romantic (domain). . In Schlegel's Viennese lectures (1809-1811), published in 1827 as On the Theory and History of the Plastic Arts, he contrasted the plasticism of Classical Art with picturesque Romanticism. He
"operated with the antinomy of terms plastic/pictorial, mechanically/ organically, finite/ infinite, and closed/accomplished. Schlegel stated that the spirit of the entire antique culture and poetry was plastic and that the spirit of modern culture, however, was picturesque (pittoresk)".-- 
These distinctions were carried over into Russian Romanticism aesthetics,
"Venevitinov objected to the indiscriminate use of the term 'pictures'. In his use of August Schlegel's term 'plastic' (plastisch, plastika) he argues for a return to the simple, primitive, enclosed, defined, limited, finite, corporeal, and plastic world of the ancients. There seem to have been two interpretations of the plastic - picturesque contrast (antitheses) in Romantic Idealist philosophy. As Venevitinov uses the contrast, and as August Schlegel intended it to be used when he defined it in Lecture I of Voslesungen uber dramatische Kunst und Literatur, it denoted the difference between the corporeal mind of the man of antiquity and the 'picturesque' mind of modern man. Ancient art appeals directly to the senses, modern art gives rise to mental pictures or images. The former is therefore real and corporeal, the latter ideal."--