In US military:
Five star = general of the army
Source: http://en.wikipedia.org/wiki/General_of_the_Army_%28USA%29
"The second version of General of the Army, also known as a "Five Star General" was created by Public Law 482 of the 78th Congress, passed on 14 December 1944, first as a temporary rank, then made permanent 23 March 1946 by an act of the 79th Congress. This was done to give the most senior American commanders parity of rank with their British counterparts. (The acts also created a comparable rank of Fleet Admiral for the Navy). The second General of the Army rank is considered separate from the 19th century version and the two are not considered comparable.
The insignia for General of the Army, as created in 1944, consisted of five stars in a pentagonal pattern, with points touching. The five officers who have held the 1944 version of General of the Army were:
• George C. Marshall 16 December 1944
• Douglas MacArthur 18 December 1944
• Dwight D. Eisenhower 20 December 1944
• Henry H. Arnold 21 December 1944
• Omar Bradley 20 September 1950"
It hasn't been granted since, although (among others) Colin Powell was considered for the position by Bill Clinton.
"The rank of General of the Army is still maintained as a rank of the U.S. military and could again be bestowed pending approval of the United States Congress. If appointed, the rank of General of the Army would carry a pay grade of O-11. Currently, official U.S. military policy is that General of the Army, General of the Air Force, and Fleet Admiral are only to be used in time of war where the commanding officer must be equal to or of higher rank than those commanding armies from another nation."
Reason for creating it was the British concept of a Field Marshal, which was the wartime supreme commander (below the queen of course), and which is technically superior to a five star, which would have meant Eisenhower having to salute a Brit. Why not call it a Field Marshal too then? mmm maybe Marshal Marshall was not such a good idea? That last is just a rumor tho.
There is even a higher rank: "General of the Armies", which is equivalent to a six star:
"The rank of General of the Armies is a title used in the United States Army as a supreme military rank considered the equivalent of a six star General. The rank has only been held twice in the history of the United States armed forces." Once of those, was even a posthumous grant to G. Washington, just to make him the most general of all generals. Not really a normal rank.
This is an excerpt of wikipedia on the term "general of the army"