OpenSubdiv is an open-source subdivision method developed by Pixar that lets you work with a high-fidelity representation of your model with great accuracy and speed. As a professional standard in the animation industry, OpenSubdiv is implemented in a variety of software packages, improving interoperability by producing the same results when models are transferred between applications. In Maya, OpenSubdiv is the default subdivision method when you preview a smoothed mesh, smooth a mesh using Mesh > Smooth, or create a subdiv proxy.
OpenSubdiv is an improved alternative to the legacy Maya Catmull-Clark subdivision method. For example, OpenSubidv takes advantage of parallel GPU and CPU structures, improving viewport performance for meshes with high subdivision levels. Additionally, in the Smooth Mesh attributes, you can turn on Displacement Preview to visualize displacement maps interactively without the need to render (see Preview the displacement results in the viewport).