Why is Sefirat HaOmer a Mourning Period?

Question: Why is Sefirat HaOmer a Mourning Period?

Many Jews celebrate on Lag b'Omer. To understand why, one must first understand why Sefirat HaOmer is a period of mourning.

Answer: During the time of the Bar Kochva revolt against the Romans, a plague killed 24,000 students of Rabbi Akiva in this seven week period between Passover and Shavuot. Over the centuries, the Jewish People experienced more tragedies (massacres, pogroms, ...) during this seven week period. To commemorate these tragedies, it has become customary to observe a period of semi-mourning during the Counting of the Omer. Weddings and other festivities are not held, music is not heard, and hair is not cut.

1. What is an Omer?
2. What is Sefirat HaOmer?
3. Why do Jews Count the Omer?
4. Why do Jews mourn during Counting of the Omer?
5. What is Lag B'Omer?
6. How do Jews celebrate Lag B'Omer?