don't ask, don't tell
phraseologicalUnit
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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.
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(by extension, often humorous) Applied to various other policies that prohibit a behavior but also discourage investigation of it.