A linear model is a mathematical representation that describes the relationship between two or more variables using a straight line. It assumes that changes in one variable will result in proportional changes in another. For example, in a simple linear regression, the model predicts an outcome based on a single predictor variable, often represented as y = mx + b, where m is the slope and b is the y-intercept. Linear models are widely used in statistics and data analysis to make predictions and understand relationships. They can be applied in various fields, including economics, biology, and social sciences, to analyze trends and inform decision-making.