In View & Raven tests - two seperate tests that are given in 2nd grade. Those tests, plus parent and teacher input and grades are used to determine giftedness. They are one part of the set of information that MCPS uses to determine giftedness as defined by MCPS.
Terra Nova - test given to 2nd graders in MCPS. Nationally normed test that shows how your kid does in relation to kids nationwide at the same grade level. This is the test that MCPS is no longer giving as of next year.
HGC admission tests - given in January for 3rd graders who apply to the Highly gifted centers that MCPS runs. Only one piece of the application data that is used to determine admission. Also determining factors is answers to application questions by families, teacher/school recommendations, and report cards.
Generally, MCPS has no program for gifted kids within the homeschool. Labeling as gifted is required by the state, but the county school system wants to make all programs accessible to all students who have demonstrated ability to do the work. So, the label doesn't really get you anything. You can apply to the HGCs without actually being labeled gifted.
--Mom to a MCPS third grader.