Indefinable Something

...Buddhism does not employ the term "soul." In order not to create the false impression that what is beyond human understanding can, in fact, be described, Theravadin teachers typically refrain from giving any name at all to whatever it is that is conscious, journeys through samsara, and is able to attain nirvana. Mahayana teachers often refer to this indefinable something as "Buddha nature," "true nature of mind," or "the clear light of awareness," terms that point to it without trying to define it. It is a teaching fundamental to both schools that the Buddha nature of every living being without exception is identical.

---The Great Compassion: Buddhism and Animal Rights, by Norm Phelps---