|  |     The sefira counts the 49 days from the second day of Passover to
    Shavuot.  When the bet hamikdash (Temple) is in existence, an omer
    is brought on each night of the sefira.  Hence, "Sefirat haOmer."
    
    It was also during this period that Rabbi Akiva's students died
    in great numbers.  A plague was sent because the students were not
    showing respect for one another.  "Students" here probably refers
    to adults.  The plague abated on Lag B'omer (33rd day of the omer).
    Hence, Lag B'omer is a day for celebration, picnics, etc.
    
    There are several mourning customs observed during part of the sefira,
    observing the deaths of R' Akiva's students.  The prevailing Ashkenazic
    custom: from 2nd of Pesach (1-omer) to 32-omer, no haircuts, weddings,
    or listening to music (except Shabbat singing).  Sefardim observe
    a slightly different 33-day period.  Chasidim and others who follow
    the kabbalistic Arizal (R' Yitzchak Luria of Tzfat/Safed) observe
    mourning customs during the entire Omer period -except- Lag B'omer;
    the difference is whether one views the customs as primarily for
    the period of mourning or as a "Chol haMoed" (half-holiday) in
    preparation for Shavuot.
    
    There is a widespread custom not to cut a boy's hair until (1) his
    third birthday, or (2) Lag B'omer following his third birthday.
    In eretz Yisrael, a huge cross-section of the country gathers on
    Lag B'omer at the tomb of R' Shimon bar Yochai in Meron, near Tzfat
    (up north).  R' Shimon was a kabbalist who died on Lag B'omer. 
    His yartzeit (death anniversary) is observed as a holiday, rather
    than a fast day, since he divulged a great deal of mystical knowledge
    just before he passed on.  I was at Meron for Lag B'omer in '81.
    It gives a young'un like me a feel for what Woodstock must have
    been like.
    
    					--- Closet Kabbalist
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|  |     First of all, Lag B'omer on Har Meron is not quite like "Woodstock",
    (I was there, hence I ain't no "young'un"(:-)), but it really is
    an experience in itself.
    
    I did do some research on the matter after work yesterday, and
    basically came up with the same findings as you, i.e. the plague
    that afflicted R' Akiva's students.
    
    Since there are many diverging opinions on the Sphirah and how to
    conduct the period of mourning, and for how long, etc., I've come
    to the conclusion that it is really up to the individual as to what
    he/she should do, and for how long a period.
    
    As for myself, I'll stick to the Pesach-Shavuot period, out of respect
    for the place of the Beit Hamigdash in Jewish history.
    
    David
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