This refers to the largest ethnic groups of Jews.
(Note: there are a lot of different ethnic/racial divisions among Jews.)
The Ashkenazi was a group of Jewish people who migrated North from the Middle East to Eastern Europe about 1000 BC. In turn, this group immigrated heavily to the United States, making it the largest ethnic Jewish group in North America.
The Ashkenazim are the ethnic stereotype most commonly associated with Judaism: dark hair, prominent eyebrows, etc. Ashkenazim is also associated with a language (Yiddish) and a set of social customs and practices that transcend race or appearance.
The name comes from the Biblical figure of Ashkenaz. Geographical areas of Jewish settlement were customarily named for Biblical figures, and Ashkenaz came to refer to the Jewish populations of Germany and France.
Why I Looked It Up
In Broad City, Alana mentions that she’s Ashkenazi several times.
The Wikipedia page for Mila Kunis notes that “her ethnicity is 96% Ashkenazi Jewish.”