What is Parameter?

Legal Definition
A parameter (from the Ancient Greek παρά, para: "beside", "subsidiary"; and μέτρον, metron: "measure"), generally, is any characteristic that can help in defining or classifying a particular system (meaning an event, project, object, situation, etc.). That is, a parameter is an element of a system that is useful, or critical, when identifying the system, or when evaluating its performance, status, condition, etc.

Parameter has more specific meanings within various disciplines, including mathematics, computing and computer programming, engineering, statistics, logic and linguistics. Within and across these fields, careful distinction must be maintained of the different usages of the term parameter and of other terms often associated with it, such as argument, property, axiom, variable, function, attribute, etc.
-- Wikipedia
Legal Definition
A value that can be defined, measured, is constant but can have variable properties, values or dimensions. A parameter is chosen commonly from a set of data, as it is important to comprehending the situation. A parameter helps in understanding a situation, while a parameter sets the boundaries of the situation.