Yes, that's correct. In the context you provided, it means that the boundaries created by water layers of different temperatures in the ocean act as a barrier that prevents the acoustic energy (sound) from dissipating or spreading out too much, allowing it to travel for enormous distances through the water.
When sound travels through a medium like water, it tends to spread out and lose its intensity over long distances due to the scattering and absorption of the sound waves by the particles in the medium. However, in the ocean, water layers of different temperatures can form distinct boundaries where sound waves experience changes in the speed of propagation and direction.
These boundaries are called sound channels, and they can act as waveguides for sound, confining and guiding the sound waves along their path. Sound waves bouncing off these boundaries can be reflected back into the channel, preventing them from dissipating and allowing them to travel long distances without losing much energy. This phenomenon is crucial for long-range underwater communication, as well as for marine animals that rely on sound for communication and echolocation.