Fast Days, The Three Weeks

What is the Jewish fast day that I heard is observed next week? When is it and what is it about? Thank you.

Shalom aleichem Rabbi Lauffer. Thank you for answering my last question. Would it be permitted to play softball on Shiva Asar b’Tammuz in the rain, or would this be forbidden because one might come to inadvertently swallow raindrops? Also, I heard there was a difference between eating food cooked on Shabbos and food cooked on Yom Kippur - the food cooked on Yom Kippur being more stringent in this case. Would food cooked b’shogeig on Yom Kippur be permitted after the fast, or would it be forbidden forever? Thanks a lot.

I read that something called “The Three Weeks” is coming soon. What does this mean? I assume it refers to a special time in the Jewish calendar. Thanks

What does Jewish Law say about fasting when you take medications? (Such as today, Taanit Esther, March 20, '19.)

On the fast day of Tzom Gedalia, a friend of mine stayed up most of the night and ate before the beginning of the fast, then slept most of the day. Is this considered cheating since he did not suffer hunger pangs during the day?