The Research Assessment Exercise is the official survey of research quality among UK higher education institutions. RAE 2008 was the first such survey since 2001 and ranked research quality in the following categories:
4* Quality that is world-leading in terms of originality, significance and rigour.
3* Quality that is internationally excellent in terms of originality, significance and rigour but which nonetheless falls short of the highest standards of excellence.
2* Quality that is recognised internationally in terms of originality, significance and rigour.
1* Quality that is recognised nationally in terms of originality, significance and rigour.
u/c Quality that falls below the standard of nationally recognised work.