Basically, brahmacarya means celibacy.
karmana manasa vaca
sarvavasthasu sarvada
sarvatra maithuna-tyago
brahmacaryam pracakshate
“The vow of brahmacarya is meant to help one completely abstain from sex indulgence in work, words, and mind—at all times, under all circumstances and in all places.” (-Yajnavalkya-smriti, as quoted in Bg. 6.13-14)
There are eight aspects of brahmacarya, as described in Shridhara Swami’s commentary on Shrimad-Bhagavatam 6.1.12:
smaranam kirtanam kelih
prekshanam guhyabhashana

