"Nature" refers to everything we are born with. In other words, Nature is everything we have and can do at the moment we're shipped brand new from the factory. It's all the base mechanisms we need to survive as individuals as well as a species as a whole. On the individual scale there's critical mechanisms which sustain an individual organism's life --, like the ability to breathe. On the species scale, there's things like individual variations from height to temperment.
"Nurture" refers to everything which has been added to or changed within us since birth. It's everything that we've learned and ways we have changed outside the normal pre-programmed life cycle from vibrant infant to elderly corpse. These are things like habits, the language we speak, the effects of acculturation to our native culture, (more or less) all individual differences in personality, and differences in height due to failure to thrive (ex. due to malnutrition).
A much more simple way to describe Nature / Nurture is to include them within the same system defined within the interdependent roles they play as two integrated parts of the same system: Nature is the structure and basic life functions of an organism, Nuture is what ensures it's survival within it's environment.
Both are required to work together to ensure the continued survival of such an organism. Nature without Nurture is symbolized by the Tarot card The Fool. Like the Fool, Nature knows nothing about it's environment by itself, and also like the Fool, that ignorance will result in a stupid, if mercifily swift, death. Nurture without Nature is like software on a DVD. It's useless without a computer to run on.To use another metaphor: Nature is like the living spaceman inside a spacesuit. Nurture is the spacesuit itself -- it's an adaption which allows the spaceman to live within a cold, airless vaccum by providing what the spaceman needs to live within that environment -- air and warmth. The spacesuit is like the knowledge of a special forces soldier trained to survive in a jungle. His knowledge provides what he needs to survive in the jungle -- food, shelter, how to avoid being eaten by a tiger -- by informing him how to find these neccessities and stay safe within in a jungle.
A Footnote I: As is obvious at this point, the debate about Nature vs. Nurture isn't really useful when the debate is framed in absolutes. There's very little in us that are solely due one or the other. For example, the ability to learn to walk at a certain age is Nature. Actually learning to walk is Nurture. It's the same with language acquisition.
Actually, to be frank, the debate isn't useful whatsoever. Nature vs. Nurture is only really useful as a lens to look at ourselves with in order to identify which parts are hardwired and which can be changed, and how these two parts within the same system are mutally interdependent and influence each other. Knowing this, it's obvious why people in every part of the world learn to speak and move, yet they learn to do so in a way unique to their culture (environment.)
Until then here's some muzak: