A parameter refers to a variable or constant in a system, model or function that can affect its nature and behavior. In mathematics, physics, computer science, engineering, statistics and other fields, parameters are usually used to describe and control the characteristics and behavior of the system.

For example, in the mathematical equation y = ax+b, a and b are parameters that determine the slope and intercept of a straight line. In physics, M and A in the mechanical equation F = ma are parameters, which determine the mass and acceleration of an object. In computer science, the time complexity and space complexity of the algorithm can also be described by parameters.

In statistics, parameters refer to some numerical values used to describe the characteristics of population distribution, such as mean, variance and standard deviation. Through the statistical analysis of sample data, we can infer the characteristics and behavior of the population by using parameters.