The month of Elul is called the "month of mercy" or the "month of Selichot," and is devoted entirely to repentance and preparation for the days of judgment-Rosh ha-Shanah and Yom Kippur.
During this month, it is customary to fulfill the commandments in the most perfect way possible, and everyone tries to make amends for one's misdeeds, to the best of one's ability.
Ta'anit Dibbur–is a "fast" of speech, in which an individual, or sometimes an entire group of people, avoid speaking of secular matters for one or several days.
Some are accustomed to hold a Ta'anit Dibbur, a "fast of speech" during this period or a part of it.
In addition to the usual one-day fasts, there were those who wished to do added penance by fasting two or three days in succession (as recorded in the books of Jewish customs from the Middle Ages on).
There were even some people who undertook to fast "from Shabbat to Shabbat," ceasing to eat or drink from the conclusion of Shabbat until the beginning of the next Shabbat.
–Rabbi Adin Steinsaltz
Adapted from A Guie to Jewish Prayer by Rabbi Adin Steinsaltz