You might have noticed that the Field Lead Source is labeled differently in the Marketo Interface. The API name is “LeadSource” with the friendly label being “Lead Source”.
In the Field Management section of the Admin panel, Lead Source is referred to as "Source"; not to be confused with the Opportunity field “Lead Source”.
Similarly to the Field Management, Lead Source is also labeled as “Source” in the column and column chooser of the Lead Database.
The Attribute in the Smart List will be labeled “Lead Source”
as well as in the Form Designer.