The definition of Saint Petersburg in the dictionary is a city and port in Russia, on the Gulf of Finland at the mouth of the Neva River: founded by Peter the Great in 1703 and built on low-lying marshes subject to frequent flooding; capital of Russia from 1712 to 1918; a cultural and educational centre, with a university ; a major industrial centre, with engineering, shipbuilding, chemical, textile, and printing industries. Pop: 5 315 000 Former names: Petrograd, Leningrad. Other definition of Saint Petersburg is a city and resort in W Florida, on Tampa Bay. Pop: 247 610.