More comprehensible information on GRADEs own website: www.gradeworkinggroup.org
See the GRADE FAQ: http://www.gradeworkinggroup.org/FAQ/index.htm
The Grading of Recommendations Assessment, Development and Evaluation (short GRADE) Working Group began in the year 2000 as an informal collaboration of people with an interest in addressing the shortcomings of present grading systems in health care. The working group has developed a common, sensible and transparent approach to grading quality of evidence and strength of recommendations. Many international organizations have provided input into the development of the approach and have started using it.
A short useful article to read is: Understanding GRADE: an introduction. Gabrielle Goldet and Jeremy Howick (2013)
A Introduction to GRADE and Summary of Findings Tables from McMaster CE&B GRADE: http://cebgrade.mcmaster.ca/Intro/index.html