It is the tenth and last day of Paryushan Parv or Dash Lakshan Dharm.
Brahmacharya means Celibacy; This means not only refraining from sexual intercourse but also includes all pleasures associated with the sense of touch, e.g. a cool breeze on a hot summers day or using a cushion for a hard surface. Again this dharma is practiced to keep our desires in check.
Brahmacharya is derived from the word Brahma - soul and charya to dwell. Brahmacharya means to dwell in your soul. Only by residing in the soul. Only by residing in the soul are you the master of the Universe. Residing outside your soul makes you a slave to desires.