Final answer:
The term 'abstract' can signify an artistic style that diverges from realistic representation or refer to intangible ideas subject to interpretation, and it is most closely defined as difficult to understand.
Step-by-step explanation:
The term abstract can be defined in various ways depending on the context in which it is used. Commonly, when referring to art, an abstract image has its roots in the real world but the artist has chosen to exaggerate certain visual elements, often deviating from realistic portrayals. In this case, abstract means that the depictions are not quite what one expects of the object in reality. It may carry an essence or notion of the subject without representing it in a literal, concrete way.
Furthermore, the concept of abstract can also involve ideas or qualities that are not tangible or concrete. For example, when discussing topics like morality or philosophical concepts, ideas like 'good' and 'evil' can be seen as abstract because they can change in meaning based on time and place, and are thus impalpable and often subject to personal interpretation or societal norms.
Therefore, when considering the options provided by the student, the definition of abstract most closely correlates to being difficult to understand, since it often deals with ideas or representations that are not directly perceived in the conventional or expected manner. This aligns with the use of the word in artistic contexts as well as in more theoretical discussions.