For each new document, the Object Styles panel lists a default set of object styles. Whenever you create an object, an object style is applied to it. By default, if you create a text frame, the [Basic Text Frame] object style is applied. If you draw a path or shape, the [Basic Graphics Frame] object style is applied. If you place an image or draw a placeholder shape that has an X in it, the [None] object style is applied. You can select a different object style to use as the default for each of these object types.
You can edit the [Basic] styles, but you cannot delete them.