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These might help.
What is a Wiki Post? - users - Discourse Meta
Create a Wiki Post - moderators - Discourse Meta
A wiki post can be created by users with a Trust Level of “Regular.” (TL3+)
Any user that has a Trust Level of “Basic” (TL1) can edit it.
It also has infinite editing time, compared to other posts.
Trust Level “New User” or TL0 have a 1-Day Editing Time Limit.
Trust Level “Basic User” or TL1 have a 3-Day Editing Time Limit.
Trust Level “Member” or TL2 have a 30-Day Editing Limit.
Trust Level “Regular” or TL3 has no difference from Trust Level Member (TL2) but you can make wikis to have an infinite Editing Time Limit.
Read more about trust levels here:
[PSA] Improved Trust Levels Guide
Guide about TL3, TL4, and moderator statuses
Understanding Discourse Trust Levels - blog - Discourse Meta