General Science tests the ability to answer questions on a variety of science topics drawn from courses taught in most high schools. The life science items cover botany, zoology, anatomy and physiology, and ecology. The earth and space science items are based on astronomy, geology, meteorology and oceanography. The physical science items measure force and motion mechanics, energy, fluids, atomic structure and chemistry.
The Armed Forces Qualification Test (AFQT) covers four sections from the Armed Services Vocational Aptitude Battery (ASVAB): Word Knowledge, Paragraph Comprehension, Arithmetic Reasoning, and Mathematics Knowledge. These four sections and your scores on them make up the Military Entrance Score, also known as the AFQT. Your AFQT score is used to determine your eligibility for entrance into the Armed Services.
The ASVAB is a series of timed aptitude tests that are used to classify selected candidates into appropriate job roles as well as ultimately decide the eligibility of candidates for US military service. In other words, perform poorly on this test and you could severely limit your opportunities in the military or even prevent yourself from serving.
One ASVAB sub-measure, the Armed Forces Qualification Test (AFQT)--which is just a separate analysis of the same tests that focuses only on four of the subtests--is also population-referenced, but its score from 1-99 is a percentile score. This means that if you score a 73, you scored as well as or higher than 73% of test-takers in the national sample.