The Counting of the Omer
10. Throughout the days of the counting of the Omer, it is customary (in
certain communities) for both men and women not to perform any "melacha"
(1) from sunset until after one counts. There is an allusion to this [in
the verse which deals with counting the Omer]: the word "shabbosos"
("weeks"), comes from the same root as the word "sh'vos," which means a
cessation of activity (2).
(1) "Melacha" in this context refers to activities such as haircuts,
bathing, and washing clothes.
(2) Another reason given for this custom is that the students of Rabbi
Akiva passed away before sunset and were buried after sunset. Since all
activities were suspended during the time of their burial, our abstinence
from "melacha," recalls the tragedy.
People who's family does not have this custom, are not required to conduct
themselves in this manner.