Generally, when scientists talk about experimentation and the scientific method they bring up what are commonly known as the variables of the experiment. The variables are the parts of the experiment that can be changed/unchanged to study their effect on the experiment as a whole. Typically, in a basic model of an experiment there are two different kinds of variables: independent and dependent.
An independent variable is a variable (or variables) that do not change or get manipulated throughout the experiment. Sometimes this is also called the controlled variable or control group.
The dependent variable(s) are those that get manipulated throughout the experiment. Typically, the hypothesis for an experiment will suggest when a dependent variable changes, the results will change. Note this may not always be the case in practice.
Example: A study is going to be performed to test how much water a new sponge will hold. The controlled variable is the size of the sponge being used. Multiple tests with sponges of the same size will need to be performed to see if they all hold the same amount of water. The dependent variable(s) is the amount of water being used for each test and what kind of environment the test is being performed in.