Don't Ask, Don't Tell was a policy of the United States military. Basically it ordered that military personnel should not ask if a serving member of the armed forces was gay or not. Those who were gay or who knew that a serving member was gay were not allowed to tell about it either. This ruling made it harder to harass any serving member of the military for being gay though what happened and happens unofficially is anyone's guess. This ruling also prevented serving service personnel from being openly gay. Bill Clinton introduced this policy which many feel was an improvement on the previous policy of banning gays from serving. Since the Clinton presidency things have progressed and today servicemen and women have been campaigning for the right to be openly gay.
The Don't Ask, Don't Tell policy was successfully challenged in Court but the court decision was appealed. The Senate finally passed new legislation allowing service personnel to be openly gay.
Senators voted 65-31 to overturn the 1993 "don't ask, don't tell" law, which bars gay people in the military from revealing their sexual orientation.
DADT is now over.