Which shaping tool helps to define and smooth out the nail's edges?

The tool that is specifically designed to define and smooth out the edges of the nails is a file. A nail file has a rough surface that helps to shape the nails by removing length or refining the edges, ensuring that the nails have a clean and polished look. It can be used to create specific shapes, such as square or round, by filing the sides and tips of the nails.

Buffers, on the other hand, are primarily used to smooth and shine the surface of the nails rather than defining the edges. They do not have the coarse texture necessary for shaping, which is why they are utilized at a later stage in the nail care process to create a glossy finish.

Nail clippers serve the purpose of cutting the nails to a desired length but do not define or smooth the edges after cutting. Meanwhile, a cuticle pusher is used to push back the cuticles and does not play a role in shaping the nail edges.

Thus, the file is the correct tool for defining and smoothing the nail's edges.