With regards to piping commands, what are the greater than (>) and less than (<) symbols called?

I usually refer to all four variations (< << > >>) as a "redirect" when speaking to folks that I know will understand.

> is used to redirect output.

$echo "hello" > file.txt

< is used to redirect input.

$ cat < file.txt

Output:

hello

>> is used to append output to the end of the file.

$ echo "world!" >> file.txt

Output:

hello
world!

<< (called here document) is a file literal or input stream literal.

$cat << EOF >> file.txt

Output:

>

Here you can type whatever you want and it can be multiline. It ends when you type EOF (We used EOF in our example but you can use something else instead).

> linux
> is
> EOF

Output:

hello
world!
linux
is

<<< (called here string) is the same as << but takes only one word.

$cat <<< great! >> file.txt

Output:

hello
world!
linux
is
great!

Note that we could have used $cat <<< great! | tee file.txt instead of $cat <<< great! >> file.txt.

They're symbols for redirection of input/output.
Quick runthrough on the differences between the redirection syntax commands