What is the key characteristic of diffraction in relation to wave propagation?

Diffraction is a fundamental phenomenon in wave propagation that describes how waves bend around obstacles and spread out after passing through small openings. This key characteristic allows waves to maintain their presence and influence even in areas where they might otherwise be blocked by physical barriers.

When a wave encounters an obstacle or a slit that is comparable in size to its wavelength, it can change direction and create a new wavefront that extends into regions that would be in the shadow of the obstacle if it were not for diffraction. This bending is crucial in various applications, such as sound waves propagating around buildings and light waves spreading out after passing through a narrow aperture.

The other choices do not accurately describe the effects of diffraction. It does not enhance wave speed, multiply frequency, or necessarily reduce intensity. Instead, it is primarily characterized by the bending effect, which is critical for understanding how waves interact with their environment.