Rabbi Simcha Weinstein writes:
Tu B’Av, the 15th Day of Av, is both an ancient and modern holiday. At one time, it marked a matchmaking day for unmarried women. In modern times, Tu B’Av has slowly evolved into a Hebrew-Jewish “Day of Love,” a little like Valentine’s Day. (…)
The Mishnah explains that women borrowed each others’ white dresses, so as not to bring shame upon those who couldn’t afford finery. On that day, the poorest woman may have ended up wearing the most expensive dress. The message to suitors was not to judge their potential brides by mere externals.
