"dummy variables" refer to variables that represent categories or groups of data. These variables are used to turn qualitative information into quantitative information so that it can be easily analyzed statistically. Full definition
It can also be resolved by introducing some of the different dummy variables to incorporate a constant measure. (essayschief.com)
Application of Principal Component Regression with Dummy Variable in Statistical Downscaling to Forecast Rainfall (scirp.org)
Running a linear regression model that includes only the votes a party receives in a local election and dummy variables indicating whether it is an incumbent government party and controlling for the party being the Liberal Democrats improves the predictive power of local elections by 40 %, reducing the average difference between the predicted and actual outcomes to 2.8 percentage points. (blog.politics.ox.ac.uk)