The process by which carbon is made in stars is known as the triple alpha process. It goes like this. First, two helium nuclei (also known as "alpha particles") fuse, making a beryllium nucleus and releasing energy to the tune of 0.09 MeV. This resulting beryllium nucleus is unstable and very short-lived, but during its brief existence, it may be struck by a third alpha particle. Now this association of a beryllium and a helium nucleus is also unstable, and in most cases, this unstable association will decay. However, it may instead turn into a carbon-12 nucleus at an excited energy level. This reaction, unlike most nuclear reactions going on in stars, is endothermic --- it requires energy, to the tune of 0.37 MeV, to get up from the ground state of the beryllium and helium nuclei to this excited state of the carbon nucleus. We shall refer to this amount of energy from here on in as the required energy. Once this has happened, the carbon nucleus will fall from its excited state to its ground state, releasing 7.65 MeV of energy. And a carbon nucleus is born. *
Now, we have said that the second transition, from beryllium and helium to carbon is rare: it only happens about four times in every ten thousand. We have also pointed out that this transition requires energy. These two statements are intimately linked: it can be shown in theory that the greater the required energy, the less likely is the leap to the excited state of carbon (and conversely, if the required energy was smaller, carbon formation would become more probable). *
And here comes the Fine-Tuning Argument. The difference between the ground state and the excited state of the carbon nucleus is, as we've said, 7.65 MeV. Now, if we could somehow change this figure --- if we could hold the ground state constant, and increase the energy difference by only 1% (i.e. 0.07 MeV), then, it is argued, the required energy to get from the ground state of the beryllium and helium nuclei to this excited state of carbon would also be increased by 0.07 MeV, making this transition virtually impossible. Hence, it is argued, the difference between the ground state and the excited state of carbon-12 is "fine tuned" to within 1% from the production of carbon, which is essential not only for the chemistry of life in itself, but also for the nuclear synthesis of heavier elements such as oxygen.
However, it has been argued that this is the wrong sum to do. The possibility of the reaction does not depend on the fact that the release in energy from the excited state to the ground state of the carbon nucleus is precisely of such-and-such a size, but on the fact that the required energy to get from the beryllium and helium nuclei to the excited carbon nucleus is fairly small. It is, therefore, this number that we should look at for evidence of fine-tuning, as has been argued by Nobel Prize-winning physicist Steve Weinberg:
Another question is about the fine-tuning. I, as I said in my talk, am not terribly impressed by the examples of fine-tuning of constants of nature that have been presented. To be a little bit more precise about the case of carbon, the energy levels of carbon, which is the most notorious example that’s always cited, there is an energy level that is 7.65 MeV above the ground state of carbon. If it was .06 of an MeV higher, then carbon production would be greatly diminished and there would be much less chance of life forming. That looks like a 1% fine-tuning of the constants of nature ... However, as has been realized subsequently after this “fine-tuning” was pointed out, you should really measure the energy level not above the ground state of carbon but above the state of the nucleus Beryllium 8 (8Be) plus a helium nucleus ... In other words, the fine-tuning is not 1% but it’s something like 25%. So, it’s not very impressive fine-tuning at all.(Here)(More from Weinberg on the Fine-Tuning Argument)
His point may be clarified by analogy: imagine a man standing on top of Mount Everest looking at a giraffe. “Such exquisite precision!” he exclaims. “Do you realise that if its head was just 1% higher above sea level, its neck would be nearly 100 meters long and it would snap under its own weight?” But the "fine-tuning" of the giraffe must be measured on the scale of the giraffe, not the mountain, and in the same way, the fine-tuning of the required energy should be measured on the scale of the required energy, not the purely arbitrary scale of the energy above the ground energy of the excited state of carbon.
I'll go with : "Chemicals which, given the right environment, catalyze their own synthesis".
There is no point in arguing over whether a definition is correct : definitions are merely convenient. Now when creationists and evolutionists argue, it is convenient for both sides to distinguish between the process of evolution and the process of abiogenesis, and this definition permits us to do so consistently.
A slight correction about the decay of protons and neutrons.
It is neutrons which decay rapidly when they're isolated: an isolated neutron will decay into a proton, a neutron, and an anti-neutrino, with a half-life for the decay of the neutron of about twelve minutes. It is neutrons, not protons, that are unstable when isolated.
Whether protons decay at all, ever, is, if I recall correctly, a controversial question, but if they do, they have an enormous half-life.