What does "arrangement" in music refer to?

"Arrangement" in music specifically refers to the process of reworking or adapting a piece of music while maintaining its original themes and ideas. This involves taking an existing composition and changing elements such as instrumentation, harmony, rhythm, or form to create a new version of the piece without altering the core musical material.

For example, a composer might take a classical symphony and create a jazz arrangement, incorporating elements of jazz harmony and idiomatic features while still preserving the original melodies and overall structure of the symphony. This allows for greater expression and performance opportunities, enabling the original work to be experienced in a fresh context.

The other options define different concepts in music. Creating an entirely new composition, improvisation, and composing for a specific instrument all refer to processes that do not involve reworking an existing piece while retaining its fundamental ideas, which is what arrangement specifically entails.