What exactly means "by..."?

来源: 于 2010-07-11 20:34:37 [博客] [旧帖] [给我悄悄话] 本文已被阅读：次

Going to purchase tickets on-line. The adv. said "... must purchase BY 7/12/2010". Does this "BY" mean that I must purchase the ticket BEFORE 7/12/2010" (that is, cannot buy it 7/12/2010)? Or, I can purchase the ticket by the end of 7/12/2010?

Thanks in advance!