Frum (Yiddish: פֿרום; [frum | frim]), from the German fromm, meaning "devout" or "pious", is a Yiddish word meaning committed to be observant of the 613 Mitzvot, or Jewish commandments, specifically of Orthodox Judaism. This appellative is used in reference to Orthodox Jews.

The opposite of frum is frei (pronounced "fry") meaning someone who is "not religious" and "free" from the yoke of the mitzvot, or feels "free" to do whatever they feel like doing.

The word "frum" can have other specific meanings depending on the context in which it is used. Often the terms frum and frei indicate one's social associations as much as his/her actual religious commitment.

Someone who is extremely frum or devout is known as a frummer.

"Frummer" can also have a negative connotation similar to "Hasid Shotah" (pious idiot), which is how the Talmud (Sotah 21B) describes a man who sees a woman drowning, however refuses to save her for he says, "it is not proper to look at her, and rescue her." A frummer in that sense is a person displaying a disproportionate emphasis on technical aspects of religion at the expense of worldly or practical concerns. A joking reference to this is found in the backronym "fiel rishus veinig mitzvos" "much wickedness and few mitzvos."

"Frum" can be used in a negative sense for: "hypocritically pious", "holier-than-thou", "sanctimonious"; or in a positive sense for: "pious", "devout", "God-fearing" and "upright". A combination is sometimes used to describe someone as "frum and ehrlich", which captures all the positive attributes of these words and would roughly mean "upright" or "righteous" (tzadik).

In orthodox communities, the acronym "FFB," meaning "Frum From Birth," is sometimes used to refer to a person who was born into a religiously-observant family and has maintained this lifestyle; it contrasts with "BT" which refers to a baal teshuva - a Jewish person from a secular background who has become religious later in life.