A sejmik was one of various local parliaments in the history of Poland and history of Lithuania. The first sejmiks were regional assemblies in the Kingdom of Poland, though they gained significantly more influence in the later era of the Polish–Lithuanian Commonwealth. Sejmiks arose around the late 14th and early 15th centuries and existed until the end of the Commonwealth in 1795, following the partitions of the Commonwealth. In a limited form, some sejmiks existed in partitioned Poland (1795–1918), and later in the Second Polish Republic (1918–1939). In modern Poland, since 1999, the term has revived with the voivodeship sejmiks, referring to the elected councils of each of the 16 voivodeships.

In modern politics, and history, a parliament is a legislative body of government. Generally, a modern parliament has three functions: representing the electorate, making laws, and overseeing the government via hearings and inquiries. The term is similar to the idea of a senate, synod or congress and is commonly used in countries that are current or former monarchies. Some contexts restrict the use of the word parliament to parliamentary systems, although it is also used to describe the legislature in some presidential systems, even where it is not in the official name.