In terms of painting composition refers to

Composition is the term used to describe the arrangement of the visual elements in a painting or other artwork. It is how the elements of art and design-line, shape, color, value, texture, form, and space-are organized or composed according to the principles of art and design-balance, contrast, emphasis, movement, pattern, rhythm, unity/variety-and other elements of composition, to give the painting structure and convey the intent of the artist.