OpenSubdiv is the default subdivision method when you smooth a mesh using Mesh > Smooth or when you create a subdiv proxy.
To smooth a mesh with OpenSubdiv
Maya smooths your mesh by adding new polygons and smoothing out vertices and their connected edges.
Adjust your smoothed mesh using the OpenSubdiv Controls.
To create a subdiv proxy mesh with OpenSubdiv
Maya smooths the selected mesh and places it inside the original, unsmoothed mesh (the proxy). Maya also creates a new group containing both meshes, and a new layer for each mesh.
Adjust your smoothed mesh using the OpenSubdiv Controls.