What is Reasonable Person?

Legal Definition
In law, a reasonable person, reasonable man, or the man on the Clapham omnibus is a hypothetical person of legal fiction who is ultimately an anthropomorphic representation of the body care standards crafted by the courts and communicated through case law and jury instructions.

Strictly according to the fiction, it is misconceived for a party to seek evidence from actual people in order to establish how the reasonable man would have acted or what he would have foreseen. This person's character and care conduct under any common set of facts, is decided through reasoning of good practice or policy—or "learned" permitting there is a compelling consensus of public opinion—by high courts.

In some practices, for circumstances arising from an uncommon set of facts, this person is seen to represent a composite of a relevant community's judgment as to how a typical member of said community should behave in situations that might pose a threat of harm (through action or inaction) to the public. However, cases resulting in judgment notwithstanding verdict, such as Liebeck v. McDonald's Restaurants, can be examples where a vetted jury's composite judgment were deemed outside that of the actual fictional reasonable person, and thus overruled.

The reasonable person belongs to a family of hypothetical figures in law including: the "right-thinking member of society," the "officious bystander," the "reasonable parent," the "reasonable landlord," the "fair-minded and informed observer," and stretching back to Roman jurists, the figure of the bonus paterfamilias, all used to define legal standards. While there is a loose consensus in black letter law, there is no accepted technical definition. As with legal fiction in general, it is somewhat susceptible to ad hoc manipulation or transformation, and hence the "reasonable person" is an emergent concept of common law. The "reasonable person" is used as a tool to standardize, teach law students, or explain the law to a jury.

As a legal fiction, the "reasonable person" is not an average person or a typical person, leading to great difficulties in applying the concept in some criminal cases, especially in regards to the partial defence of provocation. The standard also holds that each person owes a duty to behave as a reasonable person would under the same or similar circumstances. While the specific circumstances of each case will require varying kinds of conduct and degrees of care, the reasonable person standard undergoes no variation itself. The "reasonable person" construct can be found applied in many areas of the law. The standard performs a crucial role in determining negligence in both criminal law—that is, criminal negligence—and tort law.

The standard also has a presence in contract law, though its use there is substantially different. It is used to determine contractual intent, or if a breach of the standard of care has occurred, provided a duty of care can be proven. The intent of a party can be determined by examining the understanding of a reasonable person, after consideration is given to all relevant circumstances of the case including the negotiations, any practices the parties have established between themselves, usages and any subsequent conduct of the parties.

The standard does not exist independently of other circumstances within a case that could affect an individual's judgment.
-- Wikipedia
Legal Definition
This term refers to an ordinary person who exercises care while avoiding extremes of boldness and carefulness. This term does not apply the same to each as each age group behaves differently.