When students are taking linear tests, they have the option to rate their confidence level on each item.
The idea is that, on a scale of 1 to 5, how confident are you that you have chosen the correct answer?
For example, if you feel sure you are correct you might select all five stars, or if you have no idea so you are just guessing you might select only 1 star to indicate you are not that confident that you chose the correct answer.
These ratings are then viewable by your instructor(s) when viewing class test results. They can use this information to gain insight into whether or not your class's actual performance on a test matches how the students feel they performed on the test.