Sputnik (Спутник, Russian for "satellite") is a name for multiple spacecraft launched under the Soviet space program. "Sputnik 1", "Sputnik 2" and "Sputnik 3" were the official Soviet names of those objects, and the remaining designations in the series ("Sputnik 4" and so on) were not official names but names applied in the West to objects whose original Soviet names may not have been known at the time.
Spacecraft officially named Sputnik
Sputnik 1, the first artificial satellite to go into orbit, launched 4 October 1957
Sputnik 2, the first spacecraft to carry a living animal (the dog Laika) into orbit, launched 3 November 1957
Sputnik 3, a research satellite launched 15 May 1958
Spacecraft with names containing Sputnik
Being the Russian term for "satellite", the word Sputnik has appeared in the names of other spacecraft:
Dnepropetrovsk Sputnik, a series of scientific and technology development satellites
Istrebitel Sputnikov, "Destroyer of Satellites", a series of antisatellite weapons and targets
Tyazhely Sputnik, "Heavy Satellite", a failed Venus probe
Upravlyaemy Sputnik, "Controllable Satellite", a series of ocean surveillance and missile detection satellites
US-A, nuclear-powered ocean radar surveillance satellites
US-K, molniya orbit missile detection satellites
US-KS, geosynchronous orbit missile detection satellites
US-KMO, Modernised geosynchronous orbit missile detection satellites
US-P, electronic ocean surveillance satellites
US-PM, modernised electronic ocean surveillance satellites
Spacecraft designated "Sputnik" in the West