When acoustic waves encounter a barrier or narrow aperture and curve around the edges into the shadow region, this phenomenon is termed:

The correct answer is Diffraction.

Explanation:
When acoustic (sound) waves encounter an obstacle, barrier, or narrow aperture, they do not travel solely in a straight line. Instead, the wavefronts bend, curve around the edges, and spread into the geometric shadow region behind the obstacle. This bending and spreading behavior characteristic of waves is known as diffraction.

Analysis of Options:
• Diffraction: The phenomenon where waves bend and spread around obstacles or through narrow gaps into the shadow zone.
• Refraction: The change in direction of a wave as it passes from one medium into another with a different wave speed.
• Interference: The combination or superposition of two or more overlapping wave trains to form a resultant wave.
• Reflection: The bouncing back of waves upon striking a surface or boundary between two different media.

Therefore, the phenomenon where acoustic waves curve around edges into a shadow region is termed diffraction.