Jewish tradition prohibits Jews from transgressing not only the commandments of the Torah and the rulings of the sages. Jews are also prohibited from committing actions that are slightly similar to, or resemble, a forbidden act, or even have a hint of the Torah's forbidden acts. For example:
Not only backbiting (lashon hara) is prohibited, but also "avak lashon hara."
Not only idolatry (avoda zara) is prohibited, but also "avak avoda zara."
Not only lending money at interest (ribit), but also "avak ribit."