'Variables' are any factors that can be controlled, changed or measured. There are two types: the independent variable and the dependent variable. The independent variable is the condition that you change and the dependent variable is what you are observing. So if you are trying to measure the effect of water on plant growth the water would be the independent variable and the plant growth would be the dependent variable.
Independent Variable
I assume the term for something that is not changed during an experiment is called, the control. Any changes observed in the experiment, can be compare to the control, which is still be in the original form before the experiment began.
variables
control
A constant factor is one maintained unchanged throughout an experiment so that it does not affect the outcome. These are also referred to as controlled variables.
a constant
Things that are kept from changing during an experiment are invariant.
Conclusión
Control Variable
The Independent variable
The answer to your question is the Control Group.
The variable.
The rate of heat loss from the hot cup decreased during the experiment.