I am an engineer by trade, and this phrase is often used in a somewhat derogatory way to indicate knowledge which is passed around in an organization, but never documented or standardized. A Wikipedia article indicates it is used in the Six Sigma community, which is probably the reason I've been exposed to the term, but I am curious to know if it is used elsewhere, where it came from, and if others use another word or phrase for the same idea.
Tribal Knowledge is a term that can be used everywhere, because a tribe is basically a group or subgroup of people, not necessarily a division of an race. This word can be used like in this situation.
It is only generally used around corporations, businesses, offices, etc.
Synonyms include:"institutional memory," or as Martin suggested in a comment above,"institutional knowledge"
But neither of them are as well-known as tribal knowledge.
As I was reading your question a great near-synonym jumped into my mind that I first encountered in A Confederacy of Dunces: “folkways”.
If that provides a different colour to what you're looking for, I would also suggest “lore” as having different overtones to the “folklore” that another contributor already provided.
The phrase "tribal knowledge" is deprecated by people and organizations working to use more inclusive language, because of its pejorative associations. See this article in The Atlantic for a discussion of the problem, and some alternative terms. However, "tribal" isn't always viewed pejoratively, even by members of indigenous groups, as was found in an informal study related in American Indian Quarterly.
"Tacit knowledge" is another term that conveys a similar idea. Building on Mitch's comment above, the Google Ngram Viewer shows that "tacit knowledge" is far more common than either "tribal knowledge," "institutional knowledge," or "institutional memory." It also, to my ear, alludes to some of the sense of elusiveness and in-group dynamics conveyed by "tribal knowledge."