Flag Day

Definitions

1. A coordinated date when a broad change has to happen all at once across many systems or participants. In engineering slang, flag days are feared because they concentrate risk instead of letting change roll out gradually.

   In plain English: A date when a big coordinated change must happen all at once.

   Example: "They avoided a flag day migration by introducing compatibility layers, which let clients move over in stages instead of all on one nerve-racking weekend."

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