A hold-out sample is a random sample from a data set that is withheld and not used in the model fitting process. After the model is fit to the main data (the “training” data), it is then applied to the hold-out sample. This gives an unbiased assessment of how well the model might do if applied to new data.
Planning on taking an introductory statistics course, but not sure if you need to start at the beginning? Review the course description for each of our introductory statistics courses and estimate which best matches your level, then take the self test for that course. If you get all or almost all the questions correct, move on and take the next test.