Simple Explanation
Art is the product or process of deliberately arranging items (often symbolic with significance) in a way that influences and affects one or more of the senses, emotions, and intellect. It encompasses a diverse range of human activities, creations, and modes of expression, including music, literature, film, photography, sculpture, and paintings. In pixiv, everything that is created by the artist can be considered as an interpretation of an art, depending on how it's done.
Traditionally, the term art was used to refer to any skill or mastery. This conception changed during the Romantic period, when art came to be seen as "a special faculty of the human mind to be classified with religion and science". Generally, art is made with the intention of stimulating thoughts and emotions, and is presented in a way for general audience as a message.