Maybe it's easier to define Noahides by what they say they are not.
They are not, as a recent US news report contended, simply "Gentiles who act like Jews". They are not missionaries in disguise. And they are not trying to create a third path, like Jews for Jesus.
What they are, says Texas-based Noahide leader Rod Reuven David Bryant, are non-Jews who embrace the Torah through Jewish principles known as the Seven Noahide Laws.
"We're not another religion, but actually part of Judaism," says Mr Bryant, director of education and counseling at Netiv, a "centre for Torah studies" in Humble, just outside Houston. "We're a community of people on a Jewish path who want to lead fulfilling Jewish lives." Netiv's devotees include fallen-by-the-wayside Jews who have made Noahidism their means of spiritual re-engagement, Mr Bryant says.
That most of his flock is not Jewish-born tends to stymie outsiders who pigeonhole Noahides - or Bnai Noach, as they prefer to call themselves.
Even Rabbi Avraham Greenbaum, the UK-born Torah scholar who serves as Netiv's rabbinical supervisor, found the concept challenging at first: "It was a steep learning curve discovering subtle differences between Messianics, Ten Tribers, Ephraimites, Hebrew Roots, Noahides and others. But they mostly display a seriousness that many outreach rabbis could only wish for in their Jewish constituencies. These people are simply thirsting for knowledge of the Torah."
Mr Bryant, a former Christian pastor who discovered Torah after a crisis of faith, agrees. "It's not about having a thing for kippot," he says. "It's about a Jewish path, a deep desire to connect to God and the Torah."
Though perhaps less familiar than the Ten Commandments, the Noahide Laws are in the Bible: "At the dawn of human history, G‑d gave man seven rules to follow in order that His world be sustained," according to Chabad.org. Among the tenets: Respect the Creator; respect human life; respect the institution of marriage.
Following those laws are sufficient to lead a fulfilling Jewish life, Noahides like Mr Bryant contend. "Judaism's very clear that if you don't really need to convert, and you take on the sheva mitzvot, you can be part of a community of people who are Jewish," he says. "Just understand your limitations."
Those limitations, Mr Bryant explained, include not counting oneself as part of a minyan for davening, and not enjoying the right of aliyah granted to those born Jewish.
The movement is growing, says Mr Bryant, adding that Noahide groups are being launched this year in Ontario, Canada and Bristol, UK.
In the meantime, the Noahides still have a PR campaign of sorts to wage. "There are concerns that we're watering down Judaism, and concerns about marriage," Mr Bryant says. "But non-Jews' love for Torah and God inspires Yiddishkeit in the secular Jew, and more observance. I really do believe that part of the revivial of Judaism, and of inspiring Jews to be more observant, is to ask themselves why so many gentiles want to embrace their faith."