parameter
Parameter (noun) means a number or value that stays fixed while you work through one version of a calculation or experiment, but can be different in another version. Example: “In this experiment the temperature is a fixed parameter, while the pressure changes between runs.”
Fill the gap
Can you complete this real example?
In this experiment the temperature is a fixed _____, while the pressure changes between runs.
Etymology
This came into English from French paramètre, from New Latin parametrum ("parameter"), which combines Ancient Greek παρα- (para-, "beside") and μέτρον (métron, "measure").