G9
Genius
A brilliant person might be referred to as "G9," which is an abbreviation for "genius." People most often use it in email messages and on social media.
G9 is relatively obscure, so don't be embarrassed if you are unfamiliar with it. Most people who use it are nerds who love to abbreviate things, especially with coded languages like leetspeak.
An instance where you might use G9 includes when your IT guy fixes your computer, and you are grateful for his technological prowess. Another example is when your bestie comes up with an ingenious escape plan for sneaking out past curfew.
Example
Thanks for fixing my computer again, you're a G9!
A familiar sentiment among many G9s.
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To quickly say "goodnight" to someone at the end of a text or chat conversation, just send G9. This abbreviation is an informal way of signing off and wishing someone a pleasant evening.
If you don't understand why G9 means goodnight, say G9 out loud real fast. If you speak quickly enough, you should understand why some texters and chatters use G9 and goodnight interchangeably.