3ds Max uses Smoothing Groups to create hard/soft edges between smooth-shaded polygons, by "breaking" vertex normals along the edges between polygons with different Smoothing Group assignments.
Each vertex in a mesh has at least one vertex normal. Vertex normals are used to control the direction a triangle will be lit from; if the normal is facing the light the triangle will be fully lit, if facing away from the light the triangle won't be lit. When two triangles have different vertex normals along their shared edge, this creates a shading seam, called a hard edge in most modeling tools. 3ds Max uses Smoothing Groups to create hard/soft edges, while Maya uses Harden Edge and Soften Edge to do the same thing. These tools create hard and soft edges by splitting and combining the vertex normals.
How to assign smoothing groups inside of 3ds Max