What is the meaning of this sign <<<

Answer 1

I m not sure about the thing you talking about. But it could be the symbol in python interpreter which asking commands(>>) or the left shift operator(<<)
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Answer 2

Python
If you mean >>> in Python lesson
It is used to denoted the cause-and-result relationship of scripts and output.

If you are not referring to this, please share with us where you see this so we can examine and answer you accordingly.

Answer 3

In the oython console it is the sign for input
Ex.
yee@yee $ ~ python3
>>> print("hello")
hello