An independent variable is the variable that is manipulated in an expirement, study or math problem.

en.wikipedia.org/wiki/Dependent_and_independent_variables

In mathematical modelling and statistical modelling, there are dependent and
independent variables. The models investigate how the former depend on the ...

nces.ed.gov/nceskids/help/user_guide/graph/variables.asp

For example, someone's age might be an independent variable. Other factors (
such as what they eat, how much they go to school, how much television they ...

whatis.techtarget.com/definition/independent-variable

An independent variable is a variable that is manipulated to determine the value
of a dependent variables.

www.ncsu.edu/labwrite/po/independentvar.htm

Independent Variable: An independent variable is the variable you have control
over, what you can choose and manipulate. It is usually what you think will affect
...

chemistry.about.com/od/chemistryterminology/a/What-Is-The-Difference-Between-Independent-And-Dependent-Variables.htm

The difference between independent and dependent variables in an experiment
is which variable is being measured. Here's how to tell them apart.

www.sciencebuddies.org/science-fair-projects/project_variables.shtml

Science fair project variables explained - A simple introduction to dependent,
independent, and controlled variables.

chemistry.about.com/od/chemistryglossary/g/Independent-Variable-Definition.htm

This is the definition of an independent variable, with examples. An independent
variable is one of the key factors in a scientific experiment.

examples.yourdictionary.com/independent-and-dependent-variable-examples.html

The independent variables and dependent variables can vary from person to
person, and the variances are what are being tested; that is, whether the people ...

www.dictionary.com/browse/independent-variable

Independent variable definition, Mathematics. a variable in a functional relation
whose value determines the value or values of other variables, as x in the ...