Never Deploy on Friday

Definitions

A folk rule warning against deploying late in the week when support coverage and recovery time are weaker. In engineering slang, people repeat it like scripture because too many teams learned the lesson the hard way.
In plain English: A warning not to deploy late in the week when recovery support is weaker.
Example: "They ignored the 'never deploy on Friday' rule for one hotfix, and by Saturday morning half the company was learning exactly why the rule existed."