What is tc90?

As an AI language model, I am not sure what specific thing are you referring to as TC90 as it can mean different things in different contexts. Here are some possible meanings of TC90:

1. TC-90 Aircraft: The TC-90 is a military training aircraft developed by Japanese manufacturer Japan Aircraft Manufacturing Corporation (JAMCO). It is a variant of the Beechcraft King Air twin turboprop aircraft.

2. TC-90 Tape Recorder: TC-90 is a model name used by the electronics brand Sony for one of its popular portable cassette recorder/players back in the 1980s.

3. TC90 Gene: In genetics, the TC90 gene is a gene found in humans and is associated with cancer treatment and drug resistance.

4. TC-90 Weather Station: TC-90 is an abbreviation of a weather station model made by the company Oregon Scientific. It is a wireless thermometer and hygrometer that can measure temperature and humidity.

Please provide more context or information so I can give a more precise answer.