Tc is the high temperature for superconductivity. I noticed this about google a long time ago - they started "dumbing" down their search results. Don't blame them because that's where the money is, but it is annoying when you're searching for something and the results are full of celebrities because someone famous happened to say something like your search term.

https://en.wikipedia.org/wiki/High-temperature_superconducti...

The other commenter was obviously interested in the record for high-temperature superconductors. https://en.wikipedia.org/wiki/High-temperature_superconducti...

Or perhaps more generally for materials with a high Curie temperature, https://en.wikipedia.org/wiki/Curie_temperature

Disclaimer: I know absolutely nothing about this field.

Then again, Tc means different things in different fields. E.g. critical temperatures for all kinds of critical phase transitions. Note that the google search you posted above gives results for various phase transitions many of which are not superconducting phase transitions. I also was lost when I saw the original query.