Undefined.
Undefined, yet meaningful. This contradiction has been the main motif in developing Undefined Function / Object. Continually questioning the distinction between object and product, form and function, it doesn't even pretend to give a definite answer at all, as it would imply a finite outcome.
By contrast, a product tends to be the solution a designer proposes to solve a certain problem, or as an answer to some form of demand. One could argue that an object lacking this initial context has no actual reason for existence — without a clear function it would just be deemed useless.
Naturally this is not the case at all, as some of the most valuable things we keep aren't necessarily functional. Apart from art, jewellery serves as a good example of how objects go beyond function and usually even physical appearance, because of their intrinsic qualities. There must be something more, but it cannot be exactly defined.
UF/O is characterised by this notion, and more precisely, it keeps an open end to allow different interpretations. By offering a set of more or less generic objects that can fulfil both form and function, but distinctively, you're actively stimulated to ask new questions and come up with your own answers and uses.