What does “All Primes” stand for in the following context?

I am not a native English speaker and do not understand what the phrase “All Primes” mean. It is taken from the brochure “High School Magnet Programs”, table “High School Magnet Programs Admission Criteria”. The first column is “School”, the second is “essment Date(s)”. So, the second column shows the date and time of the essment, while in one case instead of time there is “All Primes”. What does it mean?