What are the numbers on the Temperature slider measuring with a RAW file?

I'm not an expert on this, but here is a good explanation of how this works:

https://community.adobe.com/t5/photoshop-ecosystem-ideas/standardization-of-color-temp-adjustments-in-adobe-cc/idc-p/15126926#M24605

In short, the numbers on the Temperature and Tint scales represent how much compensation has been made by ACR when rendering the raw file – in an attempt to make the image look right/neutral.

In the Camera Raw plugin, the Temperature slider operates in Degrees Kelvin.
In Camera Raw as a filter, the Temperature slider is a percentage scale up or down and not directly related to Degrees Kelvin.

You don't specify which Camera Raw you are speaking about.