The lower house of Poland’s parliament is called the Sejm.
The word Sejm comes from an old Polish term for a gathering or meeting. Its institutional roots reach back to medieval royal councils, while the 1493 Sejm at Piotrków helped establish a more regular parliamentary system. Historically, “Sejm” could describe Poland’s entire parliament, including both chambers.
Since the Second Polish Republic was established in 1918, Sejm has referred specifically to the lower house; the upper house is the Senate. In modern Poland, the Sejm has 460 deputies elected for four-year terms by proportional representation. Together, the Sejm and Senate form the National Assembly.
A common mix-up is assuming Sejm means the whole legislature or is another name for the Senate. It is specifically the larger, lower chamber, based in Warsaw and presided over by the Marshal of the Sejm.