I am a bit confused on the term "covariate". It seems like the term can mean two different things. In ANCOVA, the term is used for the third variable that is not directly related to the experiment. For example, the age or IQ on the performance study (comparing) between male and female in a standardized test, i.e. IQ is used as a covariate.
In ANOVA/regression design, "covariate" just refers to factors/independent variables?
I may have completely misunderstood this.
Can anyone give a simple example of the term "covariate" used in different context?