It could be related to 104(d) exempt research regulations or IRS Form 1040-ES for estimated tax.

To help me narrow down which of the 104 you are interested in, could you please tell me: Is this related to ?

That is a very specific, high volume of search results! Based on typical queries involving "104," it sounds like you might be looking for:

Is it something else entirely (like the 104-year-old advice video)?