What term, borrowed from painting, describes brief musical ideas that merge and create a vague outline?

The term that describes brief musical ideas that merge and create a vague outline is "Impressionism." This concept, borrowed from the painting movement of the same name, focuses on conveying moods and emotions rather than detailed realism. In music, Impressionism often utilizes non-traditional scales, ambiguous harmonies, and fluid forms, which mirror the techniques used by visual artists to depict light, color, and atmosphere.

Impressionist composers, such as Claude Debussy, often employed techniques such as parallel chords, whole tone scales, and soft dynamics to evoke sensations and impressions rather than specific narratives or emotions. As such, the resulting music is often characterized by its ethereal quality and the blending of distinct musical phrases, much like an impressionist painting gives a fleeting glimpse of a scene rather than a detailed depiction.

Other terms listed, like Expressionism, often convey more intense emotions and psychological depth, while Surrealism involves illogical scenes and bizarre imagery, which are not directly related to the vague outline concept in music. Romanticism, although it delves into emotion and individual expression, is typically more structured and narrative-driven compared to the fluidity and ambiguity found in Impressionism.