Rzeczpospolita (pronounced: [ʐεtʂpɔsˈpɔλita] (help·info)) is a Polish word for "republic" or "commonwealth", a calque translation of the Latin expression res publica (literally: "public affair").
The word rzeczpospolita has been used in Poland since at least 16th century, originally a generic term to denote any state with a republican or similar form of government. The famous quote by Crown Chancellor Jan Zamoyski about the importance of education is an example of this usage:
Takie będą rzeczypospolite, jakie ich młodzieży chowanie. Republics will be such as the upbringing of their youth.
Today, however, the word is used solely in reference to the Polish State (seldom also to the ancient republics such as the Roman Republic and Republic of Venice). Any other republic is referred to as republika in modern Polish.
The official name of the present-day Polish State is Rzeczpospolita Polska, which is usually translated into English as "Republic of Poland". However, such translation, when talking about the 16–18th century Poland, may be confusing since in those times the Rzeczpospolita was a monarchy. For that period, Rzeczpospolita is rendered rather as "Commonwealth" (which is another English version of the Latin res publica), as in "Polish-Lithuanian Commonwealth".
The word Rzeczpospolita is also used as a name for three periods in Poland's history:
Leaders of the currently ruling Law and Justice party have coined the term Fourth Rzeczpospolita – a new Poland they vowed to create as a replacement for the current, allegedly too corrupt, Third Rzeczpospolita.
Other expressions and names that employ the term rzeczpospolita include:
Rzeczpospolita is sometimes abbreviated to Rzplita. RP is a common abbreviation for Rzeczpospolita Polska (Republic of Poland).
The peoples that were once under Polish domination have borrowed the word Rzeczpospolita from the Polish language. Lithuanian Žečpospolita, Belarusian Рэч Паспалітая (Rech Paspalitaya) and Ukrainian Річ Посполита (Rich Pospolyta) are used only to refer to the pre-partition Polish-Lithuanian Commonwealth.

First Rzeczpospolita – the period when Poland was ruled by the nobility (szlachta) who elected the king and the parliament (Sejm); from the Nihil novi act in 1505 until the third and final partition of Poland-Lithuania in 1795;
Second Rzeczpospolita – name usually applied to the entire interwar period, from Poland's independence in 1918 until the Invasion of Poland and German-Soviet occupation in 1939, although the renascent Polish State was officially called Republika Polska until the name Rzeczpospolita Polska was introduced by the constitution of 1921 whose first article read: Państwo Polskie jest Rzecząpospolitą ("The Polish State is a Rzeczpospolita");
Third Rzeczpospolita – following the fall of the communist regime in 1989.
Rzeczpospolita szlachecka – Nobles' Commonwealth / Republic, another name for the First Rzeczpospolita;
Rzeczpospolita Obojga Narodów – Commonwealth of the Two Nations or Polish-Lithuanian Commonwealth (1569–1795);
Rzeczpospolita Babińska – a 16th-century parody of the state, established in the village of Babin, where nobles were given "offices" according to their faults instead of merits;
Rzeczpospolita Krakowska – Republic of Kraków or Free City of Kraków (1815–1846);
Polska Rzeczpospolita Ludowa or PRL – People's Republic of Poland, name colloquially applied to the whole period of communist rule in Poland, i.e. 1944–1989, although officially used only between 1952 and 1989.