Object spy is used to identify the properties, their corresponding values & the methods associated with a given object.

Since UFT 12.5, you can even use Object Spy to add objects to Object repository.

properties-methods-objectThe image above shows properties and operations available for a SIGN-ON object of class Link. Note that on Object Spy window, UFT refers  Methods as Operations.

Since UFT 14.01, object spy is no more a modal window.