.NET Standard 2.0 is a specification that defines common .NET APIs that can be used across .NET implementations like .NET Framework and .NET Core. It reduces conditional compilation by offering a common set of APIs and is more resilient to changes in platforms compared to the Portable Class Library (PCL) it replaces. .NET Standard 2.0 significantly increases the number of common APIs to over 32,000, growing 142% from the previous version, and targets a broader range of .NET implementations than PCL.