Docs-15364 invalid documents (#1450)

* DOCS-15364-invalid-documents

* DOCS-15364-invalid-documents

* DOCS-15364-invalid-documents

* DOCS-15364-invalid-documents

Co-authored-by: jason-price-mongodb <[email protected]>

Author: jason-price-mongodb

source/reference/command/validate.txt

@@ -184,11 +184,15 @@ Specify :ref:`full: true <cmd-validate-full>` for more detailed output.
 
 .. data:: validate.nInvalidDocuments
 
-   The number of invalid documents in the collection.
+   The number of invalid documents in the collection. Invalid documents
+   are those that are not readable, which means the :term:`BSON`
+   document is corrupt and has an error or a size mismatch.
 
 .. data:: validate.nNonCompliantDocuments
 
    The number of documents not conforming to the collection's schema.
+   Non-compliant documents are not counted as invalid in
+   :data:`~validate.nInvalidDocuments`.
 
 .. data:: validate.nrecords