Geek Shows were an act in traveling carnivals and circuses of early America and were often part of a larger sideshow.
The Online Etymology Dictionary give the following for "geek":
"sideshow freak," 1916, U.S. carnival and circus slang, perhaps a variant of geck "a fool, dupe, simpleton" (1510s), apparently from Low Ger. geck, from an imitative verb found in North Sea Germanic and Scandinavian meaning "to croak, cackle," and also "to mock, cheat." The modern form and the popular use with reference to circus sideshow "wild men" is from 1946, in William Lindsay Gresham's novel Nightmare ...