Tish B'Av or 9th Av

[ahka]

9th Av is the saddest day in Jewish History.  On this day happened a lot of bad things to Jewish people including the destruction of both the First Temple and Second Temple in Jerusalem.  During this day people grief, fast (no food or drink for 25 hours), and don't do anything that will bring pleasure even brush your teeth or wear leather shoes or even take a shower and say "Shalom".

Every year Jews have to grief on this day to remember all of the bad things, try to improve themselves as individuals and as people.  

Here is more info about this day in English    

История поста девятого ава

Since I am aware of this sad day I will avoid some luxury things such as eating sweets or other foods that bring pleasure.  I will eat and drink water.  I will try to learn more about this day. 

Main prohibitions

Tisha B'Av bears similar stringencies to those of Yom Kippur. In addition to the length of the fast which lasts about 25 hours, beggining at sunset on the eve of Tisha B'Av and ends at nightfall the following day, Tisha B'Av also shares the following five prohibitions:^[6]

1. No eating or drinking
2. No washing or bathing
3. No application of creams or oils
4. No wearing of leather shoes
5. No marital relations

These restrictions are waived in the case of health issues. For example, those who are seriously ill may eat and drink, in contrast to Yom Kippur, when eating and drinking is allowed only in cases of life-threatening need.^[7] (On other fast days almost any medical condition may justify breaking the fast; in practice, since many cases differ, consultation with a rabbi is often necessary.) Ritual washing up to the knuckles is permitted. Washing to cleanse dirt or mud from one's body is also permitted.