a finish of a race in which two or more contestants are so close to the finish line that reference to a photograph of the finish is necessary to determine the winner.
Origin
1935-40
Related forms
photo-finish, adjective
British Dictionary definitions for photo finish
photo finish
noun
1.
a finish of a race in which contestants are so close that a photograph is needed to decide the result
2.
any race or competition in which the winners or placed contestants are separated by a very small margin