The jurisprudential definition of "negligence"

Salmond on Jurisprudence
Sweet and Maxwell, 12 Ed.
p 380
Negligence
Negligence is culpable carelessness. “It is”, says Willis J, “the absence of such care as it was the duty of the defendant to use.” What then is meant by carelessness ? It is clear in the first place that it excludes wrongful intention. There are two contrasted and mutually inconsistent mental attitudes of a person towards his acts and their consequences. No result which is due to carelessness can have been also intended. Nothing which was intended can have been due to carelessness.
It is to be observed, in the second place, that carelessness or negligence consists in thoughtlessness or inadvertence. This is undoubtedly the commonest form of it, but it is not the only form.
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When I consciously expose another to the risk of harm, and harm actually ensues, it is inflicted not wilfully, since it was not desired, nor inadvertently, since it was foreseen as possible or even probable, but nevertheless negligently. If I do harm, not because I intended it, but because I was thoughtless and did not advert to the dangerous nature of my act, or foolishly believed that there was no danger, I am certainly guilty of negligence.
Negligence then is failure to use sufficient care, and this failure may result from a variety of factors.
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p.386 Liability

We have already seen that in assessing whether a man is guilty of negligence regard must be had to the seriousness of the danger to which his actions expose others, to the degree of probability that the danger should occur and to the importance of the object of the defendant’s own activity. Clearly the greater the danger and the greater its likelihood, the greater the defendant’s carelessness in not taking precautions against it, and conversely the more important and socially valuable his own objective, the smaller his carelessness.