Depth of Knowledge also referred to as D.O.K., is the complexity or depth of understanding required to answer or explain an assessment related item or a classroom activity. The concept of depth of knowledge was developed through research by Norman L. Webb in the late 1990’s. Webb was a senior research scientist at the Wisconsin Center for Education Research.
There are several pieces to D.O.K.
How does this relate to Common core?
From an article at Edutopia they attempt to provide some explanation and detail
If you want to get into depth give this article a read: common-core-state-standards-rigor