What is `>&2` used for?

Question

I am asking in the context of piping the result of the following command to another:

echo "foo" | tee >&2

Answer 1

with >&2 you are sending the output to standard error instead of standard out.

here you can read about the standard I/O streams:

https://man7.org/linux/man-pages/man3/stdin.3.html