"Similar" lists the rows whose [[Invantive Studio/Repository/Concepts/Natural Key|natural key]] is similar to that of the selected row, for instance to find a table with almost the same name. Choosing a row from the list opens its summary window. When there are none, the list reads "No similar objects.". It is on the context menu of a row in a list, and on the toolbars of the details of a row and of the property pane.