[se4u]

When a qualifying noun is absent , then priors means prior beliefs.

[xyzsparetimexyz]

Prior to what? Why not just say beliefs?

[niek_pas]

"Update your priors" is a common expression in English: https://en.wiktionary.org/wiki/update_one%27s_priors#English

[staticman2]

Your wiktionary link indicates it is not a common expression in English but instead something "rationalist community" people say.

[pocksuppet]

HN is a rationalist community hangout.

[repparw]

we're reading comments on a post about math proofs

[rob]

No it's not. Where do you come up with this? Just because you searched the phrase on Google and there's a single result for it on a wiki? Who do you know that's using this expression regularly?

[eudamoniac]

https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que...

[happytoexplain]

"Common" is an exaggeration.