What is strict search:
By defalut, search working not strictly. For example, if you are looking for persons who is 1.50m. - 1.60m. height, in results you will see those, who specified his or her height and it's lying in this interval, and those who didn't specified height at all, but still potentialy can be tall or short enough for you.
If you would like to search ONLY those, who specified necessary parameter and that parameter suits you, you should check Strict search checkbox.