In English, kasha usually refers to the pseudocereal buckwheat or its culinary preparations. In Eastern European cuisine, kasha can apply to any kind of cooked grain. It can be baked but most often is boiled, either in water or milk, and therefore the term coincides with the English definition of 'porridge', but the word can also refer to the grain before preparation, which corresponds to the definition of 'groats'. Kasha is eaten widely in Belarus (каша), the Czech Republic (kaše), Lithuania (košė), Poland (kasza), Romania and Moldova (cașa), Russia (каша), Slovakia (kaša), Slovenia (kaša), Kazakhstan, and Ukraine (каша), where the term, besides buckwheat, can apply to wheat, barley, oats, millet, rye and even rice. Kasha has been an important element of Slavic diet for at least 1,000 years. This English-language usage probably originated with Jewish immigrants, as did the form קאַשי kashi (literally translated as "porridges").

In Ashkenazi Jewish culture

As an Ashkenazi-Jewish comfort food, kasha is often served with onions and brown gravy on top of farfalle, known as kasha varnishkes. Kasha is a popular filling for knishes and is sometimes included in matzah-ball soup.

In Czechia

In Czech the cognate kaše has a wider meaning that also encompasses mashed potato (bramborová kaše), pease pudding (hrachová kaše), etc.

In Poland

In Polish, cooked buckwheat groats are referred to as kasza gryczana. Kasza can apply to many kinds of groats: millet (kasza jaglana), barley (kasza jęczmienna), pearl barley (kasza jęczmienna perłowa, pęczak), oats (kasza owsiana), as well as porridge made from farina (kasza manna). Bulgur can be also be referred to as a type of kasza in Polish (kasza bulgur). As Polish blood sausage is prepared with buckwheat, barley or rice, it is called kaszanka (kasha sausage). Annual per capita consumption of groats in Poland was approximately 1.56 kg per year in 2013.

In Russia

The largest gross buckwheat consumption per capita is in Russia, with 15 kg per year, followed by Ukraine, with 12 kg per year. Buckweat comprises 20% of all cereal consumption in Russia. In Russian, buckwheat is referred to formally as гречиха, or colloquially as гречка , which gave rise to the Yiddish words gretshkes/greytshkelach and retshkes/reytshkelach. Kasha is one of the Russian traditional dishes. Together with shchi it used to constitute staple foods for poorer people. This fact is commemorated in the Russian saying, "щи да каша – пища наша", which literally translates as "shchi and kasha are our food". Butter is often eaten with most kasha recipes, hence another Russian saying: "кашу маслом не испортишь", which translates to "you won't ruin kasha with butter".