A controlled experiment is a scientific test where researchers change one variable while keeping all other conditions the same. This helps to determine if the change in that specific variable causes any effect. For example, if scientists want to test how light affects plant growth, they might grow two groups of plants, one in sunlight and the other in darkness, while keeping factors like water and soil consistent. In a controlled experiment, the group that receives the treatment is called the experimental group, while the group that does not is the control group. By comparing the results from both groups, researchers can draw conclusions about the impact of the variable they changed.