What is a shift from one key to another within the same composition?

A shift from one key to another within the same composition is known as a modulation. This musical technique involves changing the tonal center, which can create contrast, tension, or surprise within the piece. Modulations can be smooth or abrupt, and they often serve to enhance the emotional or thematic development of the music. Common types of modulation include direct modulation, common chord modulation, and sequential modulation.