| June 14, the anniversary of the day (June 14, 1777) when Congress adopted the Stars and Stripes as the national flag of the United States. |
Flag Day  (flāg)  n. June 14, observed in the United States in commemoration of the adoption in 1777 of the official U.S. flag. |
flag day jargon
A software change that is neither forward- nor backward-compatible, and which is costly to make and costly to reverse. E.g. "Can we install that without causing a flag day for all users?"
This term has nothing to do with the use of the word flag to mean a variable that has two values. It came into use when a massive change was made to the Multics time-sharing system to convert from the old ASCII code to the new one; this was scheduled for Flag Day (a US holiday), June 14, 1966.
See also backward combatability, lock-in.
[The Jargon File]
(1998-01-15)
Flag Day
in the United States, a day honouring the national flag, observed on June 14. The holiday commemorates the date in 1777 when the United States approved the design for its first national flag
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