Judicial reviews challenge the lawfulness of the way in which a decision has been made by a public body.
In this case the Wikimedia Foundation and a Wikipedia editor tried to challenge the way in which the government decided to make regulations covering which sites should be classed "Category 1" under the Online Safety Act - the strictest rules sites must follow.
It argued the rules were logically flawed and too broad, meaning a policy intended to impose extra rules on large social media companies would instead apply to Wikipedia.
In particular the foundation is concerned the extra duties required - if Wikipedia was classed as Category 1 - would mean it would have to verify the identity of its contributors, undermining their privacy and safety.
The only way it could avoid being classed as Category 1 would be to cut the number of people in the UK who could access the online encyclopaedia by about three-quarters, or disable key functions on the site.
The government's lawyers argued that ministers had considered whether Wikipedia should be exempt from the regulations but had reasonably rejected the idea.