parameter of the Standard Model

generate a one-sentence description for a given conceptual class.
# Response Format
Return only the sentence: "Description: [one-sentence description of the conceptional class]"

Class: parameter of the Standard Model

A parameter of the Standard Model is a fundamental numerical input—such as a particle mass, coupling constant, or mixing angle—whose value is not predicted by the theory itself but must be determined experimentally to fully specify its physical predictions.