Israeli (zionist) Hebrew uses the word “Dati” as equivalent to the word “religious” in English. When used for a Jew, it would indicate that person is basically frum (at the minimum Shomer Shabbos and Shomer Kashrus). “Hareidi” (what in English is frequently translated as “Ultra-Orthodox”) is a type of “Dati” (all Hareidim are Dati’im, but not the reverse). Defining “Hareidi” is almost impossible (based on clothings or hairstyle?, how one votes?, if one is for or against the Medinah? etc.).
Note that in Yiddish, there are no equivalent words, since the concepts didn’t exist. The distinction is alien to Jewish tradition.