A kolach or kalach is a traditional bread found in Central and Eastern European cuisines, commonly served during various special occasions – particularly wedding celebrations, Christmas, Easter, and Dożynki. The name originates from the Old Slavonic word kolo (коло) meaning "circle" or "wheel". Korovai is sometimes categorised as a type of kolach.

The name slightly varies between countries, but its general meaning originally comes from the Early Slavic root vocabulary that references the circular shape of the bread (Proto-Slavic: *kolačь, derived from "kolo"). Variants of "kolach" (Bulgarian, Macedonian, and Ukrainian: колач, Polish: kołacz, Silesian: kołocz, Romanian: colac, Serbian: колач / kolač, Slovene: kolač) are the most commonly used forms, but "kalach" (Belarusian, Russian, and Ukrainian: калач, Hungarian: kalács) is also widespread. The Albanian: kulaç is cognate with all of these.

The nouns "korovai" (Polish: korowaj, Serbian: коровај, Ukrainian: коровай), "karavai" (Belarusian: каравай, Russian: каравай), and "kravai" (Bulgarian: кравай) are not etymologically related to "kolach", but are used as names for a very similar type of bread, one that can be savoury or sweet; in some countries, such as Poland, korowaj is considered simply a more decorative type of kolach and thus used interchangeably with kołacz.

The names Czech: koláč and Slovak: koláč, although of the same origin as "kolach", refer to another pastry—the differently shaped cake kolach as opposed to the sweet bread. In Poland and Serbia kołacz and kolač respectively are also used as the name for different types of cakes.

Kolach and korovai pastries, as well as the customs associated with them and the way they are made, share some similarities (especially across the Slavonic nations), but various differences exist between countries and even regions within each country.

Just like in neighbouring Ukraine and Poland, the kolach remains an important element of rural celebrations in Belarus (especially at weddings) where it is known as "калач" and "кравай". The kalach represents hospitality, future prosperity, and respect; it is often decorated with various figurines and symbolic flags. Usually served savoury, the kravai is sometimes dipped in salt.

The Hungarian kalács (pronounced [ˈkɒlaːtʃ]) is a sweet bread very similar to brioche, usually baked in a braided form, and traditionally considered an Easter food. Until the end of the 19th century, the preparation of kalács was similar to that of everyday bread; the difference was in the shape, and in the better/quality flour used for the kalács. Nowadays kalács is prepared from dough enriched with milk and eggs. It is baked in an oven or brick oven, sometimes directly on the stones of the brick oven, or on a baking sheet.

Kalács is part of the traditional Easter menu in Hungary, often consecrated together with ham in Catholic churches. Kalácskoszorú is the circular form of the kalács is most commonly made for Easter. Another version is also the kalács-kifli. Kalács is also common inside a komatál, a traditional gift plate, given to someone as a gesture of friendship. In the Szeged region at All Saints unfilled kalács was baked called All Saints' Kalács (mindenszentek kalácsa, kolduskalács = Beggar's Kalács), which was given to beggars at the gate of the graveyard. Also kalács was given to beggars praying at the graveyard's gate in Csallóköz to prevent the dead from returning. Giving kalács to beggars is the Christian form of the pagan tradition of treating the dead.