A policy of the U.S. military from 1993 to 2011, which barred openly gay, lesbian, or bisexual people from serving in the military, while also barring discrimination against closeted gays, lesbians, and bisexuals.
(by extension, often humorous)Applied to various other policies that prohibit a behavior but also discourage investigation of it.
The actual "don't ask, don't tell" policy did not forbid investigation into a service member's sexuality; rather, it required that there be credible evidence of homosexual behavior, or of intended homosexual behavior, before an investigation could be launched. (This contrasted with the previous policy, whereby military applicants were explicitly asked about their sexual orientation.) However, it was widely misunderstood among the civilian public as forbidding all investigation, and it is this understanding that underlies most extended and allusive uses.