public Vector2 adjacentEnd { get; set; }

An edges shape is comprised of multiple edges (line segments) defined by all its vertices. However, when a collision occurs with the end vertex of the shape then this vertex can be used to form a collision normal, and calculate the collision response. This allows for joining of individual edge shapes to produce a continuous collision surface.

This property is identical to EdgeCollider2D.adjacentEndPoint. It is only used when the shapeType is PhysicsShapeType2D.Edges and useAdjacentEnd is true.