I think its several properties that make the defenition:

a checked out document  has a property  called :
urn:schemas-microsoft-com:publishing:IsCheckedOut - True

a published  document has these properties:
urn:schemas-microsoft-com:publishing:documentstate - approved
urn:schemas-microsoft-com:publishing:hasbeenapproved - True
urn:schemas-microsoft-com:publishing:publishedby - CALANIT\ishais

I dont know if it the only differences- if i were you i'd check further. use
this code to get all the properties of a document:
Sub test()
On Error Resume Next
Dim odoc As New PKMCDO.KnowledgeDocument
odoc.DataSource.Open "
<CHSRV04/.../ttt.itm>" target="_blank" rel="nofollow">CHSRV04/.../ttt.itm>
CHSRV04/.../ttt.itm"
For i = 1 To odoc.Fields.Count
Debug.Print odoc.Fields(i).Name & " - " & odoc.Fields(i).Value
Next
End Sub

Use it one with a published,a checkedout and a checked in (non published)
documents and compare the properties.