There are four types of Celibates-brahmacharis.
The first is called savitra, which refers to a celibate-brahmachari who, after initiation and the sacred thread ceremony, must observe at least three days of celibacy.
The next is called prajapatya, which refers to a celibate-brahmachari who strictly observes celibacy for at least one year after initiation.
The next is called brahma-brahmachari, which refers to a celibate-brahmachari who observes celibacy from the time of initiation up to the time of the completion of his study of the Vedic literature.
The next stage is called naisthika, which refers to a ceilbate-brahmachari who is celibate throughout his whole life.
Out of these, the first three are upakurvana, which means that the brahmachari can marry later, after the brahmachari period is over. The naisthika-brahmachari, however, is completely reluctant to have any sex life; therefore the Kumaras and Narada are known as naisthika-brahmacharis. Such brahmacharis are called vira-vrata because their vow of celibacy is as heroic as the vows of the kshatriyas. The brahmachari system of life is especially advantageous in increasing the power of memory and determination. It is specifically mentioned in this connection that because Narada was a naisthika-brahmachari he could remember whatever he heard from his spiritual master and would never forget it. One who can remember everything perpetually is called a shruti-dhara. A shruti-dhara brahmachari can repeat verbatim all that he has heard, without notes and without referencing books. The great sage Narada has this qualification, and therefore, having taken instructions from Narayana Rishi, he is engaged in propagating the philosophy of devotional service all over the world. Because such great sages can remember everything, they are thoughtful, self-realized and completely fixed in the service of the Lord.
Ref >> Srila Prabhupada Vani