Although occasionally used to describe any type of sports facility, "Concrete Doughnut" is usually reserved as an epithet for the multipurpose stadiums built in the United States and Canada during the 1960's and 1970's. A concrete doughnut is characterized by a perfectly round exterior, completely enclosing a perfectly round playing field, usually covered with Astroturf. The perfectly round shape made such a facility suitable for the addition of a dome.
Precursors to the concrete doughnuts were partial-circle stadiums such as Cleveland Municipal Stadium and Shea Stadium in Queens, New York. When the Houston Astrodome opened in 1962, it was billed as the "Eighth wonder of the world." People were entranced by the "futuristic" look of these facilities, and so concrete doughnuts went up all over the country:
The Oakland Coliseum was a partial ring which opened in 1966. There are concrete doughnuts used as football (soccer) venues all over the world, but someone else will have to list them.
The concrete doughnuts' advantages were: a high seating capacity, access from all sides, the ability to use standardized seating all the way around and sight lines were equally good. A dome removed the possibility of a rainout. Most importantly, both football (American) and baseball could be played in them, saving tens of millions of dollars over building separate facilities for each.
Of course, all of the sight lines in a concrete doughnut were equally bad, and making a facility sports-neutral removed all of its personality. They were suited more for football than for baseball. The abomination of astroturf need hardly be discussed here.
Concrete doughnuts were a signal that sports teams were beginning to emphasize profit over product; reporters and fans began to speak out against them. This aversion was a factor in Baltimore's refusal to build a new domed stadium for the Colts in the late 1970's, with all of the consequences that followed.
A notable exception to the concrete donut fad was Royals Stadium, now known as Ewing Kaufmann Field, which opened in Kansas City, Missouri in 1973 to house the Kansas City Royals. The move away from concrete doughnuts began in earnest when Oriole Park at Camden Yards (designed by HoK, the same firm that designed Royals Stadium) opened in 1992. In the United States, at least, the trend now is for separate sports facilities tailored to particular sports - lozenge-shaped stadiums for football, and idiosyncratic facilities for baseball.