13:37, the internet's own minute
A number that means fluency, written in a code invented to get past word filters.
Where the number comes from
Leetspeak substitutes numerals for letters: 1 for L, 3 for E, 7 for T. Spelled that way, 1337 reads as leet, short for elite.
The substitution began as a practical measure on bulletin boards and early chat systems, where filters blocked certain words outright. Writing around the filter became a marker of who had been there long enough to know the conventions.
From evasion to in-joke
The original need disappeared as moderation changed, but the notation stayed because it had become a signal rather than a workaround. Using it correctly showed you knew the culture; using it too earnestly showed you did not.
By the time 1337 was widely recognised it was mostly ironic, which is the usual fate of a shibboleth that escapes its original community.
The minute
13:37 arrives once a day on a twenty-four hour clock, in the early afternoon. To most people it is an unremarkable time. To a particular generation of the internet it reads instantly as a joke, which is exactly the property that makes it worth having.