The test of General Educational Development (GED) is given to adults who did not receive a high school diploma.  It is written and administered by the GED Testing Service of the American Council on Education.  Once a student has passed the GED, they receive a certificate of completion that is equivalent to a high school diploma.
While the GED covers the same subject matter as what is studied in an American high school, the tests are designed to appreciate a student’s ability to read and process information in the five subject areas tested: Writing Skills, Social Studies, Science, Interpreting Literature and the Arts, and Mathematics.  The GED does not attempt to test all of the information in these subject areas that is taught in the four years of high school. Instead it seeks to ascertain if the student has the same comprehension, evaluation, application, and analysis skills he or she would have acquired from completing high school.
The GED is given in five sections, mirroring the five subjects.  The highest possible score for a single section is 80 points.  The number of points needed to pass each section and needed for a total score vary from state to state.  Most states require that a student score 40 points to pass a section, but must have a total score of 225 points, meaning he or she needs to average 45 points on each section.   The test sections are broken down as follows:
 
 

You can access more information about the GED from the official GED Testing Service website at www.gedtest.org.  The site has sample questions and instructional guidance, links to local testing centers, scoring and regional policies, scores needed to enter college, plus a ton of other helpful information concerning the GED.