Quantitative variables are types of variables that can be measured and expressed numerically. They represent quantities and can be classified into two main categories: discrete and continuous. Discrete variables take on specific values, such as the number of students in a classroom, while continuous variables can take any value within a range, like the height of individuals. These variables are essential in fields like statistics and research, as they allow for mathematical calculations and statistical analysis. By using quantitative variables, researchers can identify patterns, make predictions, and draw conclusions based on numerical data.