sefirah
Noun
Meaning
(Kabbalah) Each of the ten attributes that God created, through which he can project himself to the universe and man.
(Judaism) The counting of the omer, that is, the period of 49 days between Passover and Shavuot.
Source: en.wiktionary.orgExamples
By Ashkenazi practice, the semi-mourning observed during the period of Sefirah (see above) is lifted on Lag Ba'Omer, while Sefardi practice is to lift it at the end of Lag Ba'Omer.
See, for example, citation Sefirah has long been observed as a period of semi-mourning.