In general terms, what is an experimental group?

In social science, we often speak of two kinds of groups when it comes to experiments: the control group and the experimental group. Imagine you're told that marigold plants grow better in the shade than in the sunlight, as was previously believed. This is a hypothesis that you need to test. You would do so by placing some marigold plants in the sun, as always, and placing some marigold plants in the shade; you'd then see if the plants in the shade grow better than the ones in the sun. The plants in the sun are the control group and the plants in the shade are the experimental group. Thus, the group receiving the variable being tested is the experimental group and the group that does not receive the variable being tested (in this case, shade) is the control group. In other words, the experimental group is subject to the changes in the independent variable that is being tested and, by means of this, a new intervention or treatment is tested.