An integer that uniquely identifies each document in an index.

public int DocId;

Public DocId As Integer

Each document in an index is assigned a unique integer identifier called a "DocId" or document id. The first document added to an index has the DocId 1, and subsequent documents will have sequentially numbered DocIds 2, 3, 4, and so forth. When a document is reindexed, its DocId is "cancelled" and a new DocId is assigned. Compressing an index renumbers all of the DocIds, so after an index has been compressed, a document's DocId may change.  

DocIds are used in: