Is there a generally agreed upon idea of what Buddha nature is? I often hear and read about Buddha nature. 

I wonder, is Buddha nature something common to all varieties of Buddhism? And where in the scriptures can I find out more about this? I'm asking because sometimes when I hear about it, it sounds a bit like the idea of atman as brahman: which I don't understand, because how can that be compatible with anatman and emptiness?
I'm asking because sometimes when I hear about it, it sounds a bit like the idea of atman as brahman: which I don't understand, because how can that be compatible with anatman and emptiness?


It can be understood in different ways, dependent on tradition. 

It certainly does not mean that there is a soul, an experiencing entity or an inner core. Remember that this is just a word, a convention. 

When practicing insight meditation, one will realize that it cannot mean that there is an atman. It is only when such deep doctrines are treated intellectually, that there arises confusion. These profound doctrines cannot be grasped by the intellect. They can only be understood experientially.


  Is there a generally agreed upon idea of what Buddha nature is?


One meaning is, that every being has the capacity to win Nibbana. 

Nibbana is already there but its covered in thick layers of ignorance (avijja) and has been plastered over with concepts and conventions.

The unconditioned state is an existing reality, that can be experienced when the meditator has done away with ignorance, clinging and attachment and cultivated the paramitas to full maturity.