Linear models are mathematical representations that describe the relationship between a dependent variable and one or more independent variables using a straight line. The simplest form is the linear regression model, which predicts outcomes based on the equation y = mx + b, where y is the dependent variable, m is the slope, x is the independent variable, and b is the y-intercept. These models are widely used in various fields, including economics, biology, and engineering, to analyze trends and make predictions. They assume a constant relationship between variables, making them easy to interpret and implement, especially when the data shows a linear pattern.