- Peninei Halakha
It is customary to rejoice somewhat on Lag Ba-omer. Even though we observe some customs of mourning during the omer period, nevertheless, one may sing and dance on Lag Ba-omer. Taĥanun is recited neither on Lag Ba-omer nor at Minĥa on the preceding day. One may not fast on Lag Ba-omer.
The reason we rejoice on Lag Ba-omer is that the Rishonim had a tradition that the students of R. Akiva stopped dying on the 33rd day of the omer (Me’iri, Yevamot 62b; sa 493:2). Some explain that his students actually continued dying, but on the 33rd day of the omer R. Akiva began teaching new students – including R. Shimon bar Yoĥai – who did not die in the plague, and through them Torah spread among the Jewish people. This is why we rejoice on Lag Ba-omer (Pri Ĥadash 493:2). Others claim that on the 33rd day of the omer R. Akiva conferred rabbinic ordination on his five new students – R. Meir, R. Yehuda, R. Yosi, R. Shimon bar Yoĥai, and R. Elazar b. Shamu’a – who continued the tradition of Torah (Kaf Ha-ĥayim 493:26, based on Sha’ar Ha-kavanot). Another reason for rejoicing on Lag Ba-omer is that it is the yahrzeit or hilula of the holy Tanna R. Shimon bar Yoĥai, who was R. Akiva’s disciple.
We will first summarize briefly the customs of mourning and rejoicing that apply on Lag Ba-omer. According to all customs, one may sing, dance, and play musical instruments on Lag Ba-omer, from beginning to end. Regarding weddings and haircuts, the matter depends on one’s custom. According to the customs of Ashkenazic and some Sephardic communities, one may get married and cut one’s hair during the day of Lag Ba-omer, and some permit these activities even at night. According to the custom of most Sephardim, however, one may not get married or cut one’s hair on Lag Ba-omer (see above 3:4-5). Nonetheless, when Lag Ba-omer falls out on Friday, one may cut one’s hair in honor of Shabbat, even according to Sephardic custom (sa 493:2). Those who follow the customs of Arizal do not cut their hair on Lag Ba-omer even in this situation, because they refrain from cutting their hair throughout the omer period, until Erev Shavu’ot (Kaf Ha-ĥayim 493:13).
 Although one may not fast on Lag Ba-omer, a bridegroom does fast (ma 573:1). Some say that even a bridegroom does not fast (Mishmeret Shalom §38). Levush, Pri Megadim, and others state that one does not recite Taĥanun at Minĥa on the previous day. Ĥok Yaakov, however, rules that one should recite it. See Kaf Ha-ĥayim 493:28. It seems that the prevalent custom is to omit it.