What reference/import doI need for stdole.IUnknown

I'm converting VBA script code to .net and am not all that familiar with it.

My class contains
Public ReadOnly Property NewEnum() As stdole.IUnknown
Get
NewEnum = m_Terms.GetEnumerator
End Get
End Property

I'm getting an error:
Error 11 Type 'stdole.IUnknown' is not defined.

Do I need a reference or an import statement?

PS:Is there a reference /web site that's helpful for finding such info?

Thanks
CJ