What exactly is svabhava?

What exactly is svabhāva in Nagarjuna's Madhyamaka? It is translated as inherent nature or inherent existence or inherent substance. But what does that **really** mean? Does it carry the same meaning as being unconditioned? If yes, then Nirvana and the Buddha's Dharma, being unconditioned, must have svabhāva. But they don't, according to Madhyamaka. Why does a chair or a photon or empty space or concepts or the Dharma (teachings) or Nirvana have no svabhāva? From the Wikipedia article on Madhyamaka, it sounds like something that is unconditioned has svabhāva. But that's not right according to Madhyamaka. > Nagarjuna's critique of the notion of own-nature > argues that **anything which arises according to conditions, as all > phenomena do, can have no inherent nature, for what is depends on what > conditions it.** Moreover, if there is nothing with own-nature, there > can be nothing with 'other-nature' (para-bhava), i.e. something which > is dependent for its existence and nature on something else which has > own-nature. Furthermore, if there is neither own-nature nor > other-nature, there cannot be anything with a true, substantial > existent nature (bhava). If there is no true existent, then there can > be no non-existent (abhava).