Re-topology is the process transforming messy meshes into quad-dominant topology without altering object shape, often after sculpting.

Re-topology is the process transforming a mesh topology (the way the edges flow to form faces) without altering its overall basic shape.

It is generally used after sculpting, boolean operations, operations that leave non quad dominant meshes, or otherwise messy topology originating from other applications like CAD models or 3D scans.

It converts triangulated meshes or ngons into a clean quad-dominant topology adequate for animation or texturing through unwrapping