An objective test is like a game where you have to answer questions. There are no opinions or guesses. The questions have only one answer and it's always the same.
It's like when you are asked how much is 2 plus 2, and you know the answer is 4. There's no other answer.
Objective tests are used in school to see how much we learned and if we understood the things we studied. They are also used in job interviews to test if we have the skills required for the job.
Some examples of objective tests are multiple-choice questions or true or false questions, where you have to choose the correct answer. These tests help us know how well we do in school or at work.