Tisha B'Av is only observed by the Jewish people, and because of the significance and the peculiarity of the day, Jewish people are always committed to observing the day with sincerity. There are prohibitions that guide how the period should be observed, and most of these prohibitions are what you will see an average Jewish person do during Tisha B'Av. Tisha B'Av simply means the ninth day of the month of Av on the Jewish calendar. In English calendar, the day will be observed on the 10th of August, 2019.
This is the period where Jewish people remember the greatest calamities that had ever befallen them. Jewish people observe this period by fasting, mourning and through prayer. The destruction of the first temple built by King Solomon, and the destruction of the second temple built by Ezra and Nehemiah for Jerusalem are parts of many things to be remembered during Tisha B'Av.
For the most part, the religious remembrance day is remembered only by Jewish people. However, that is not to say that no one else honors this day. There are probably others or individuals who may remember this day because it means something to them.
It could also be remembered by people who do not practice Judaism because the tragedies that are remembered on this day also has an impact on these people’s lives and they want to spend time remembering those who died. This seems like a perfect day to do that. However, the day is set aside for those who practice Judaism. The people who practice Judaism are known as Jews. Therefore, the Tisha B’Av is significant to the Jewish people.