It seems like "hj" is likely a typo or an abbreviation rather than a standard English word. If you meant "hi," it is a casual greeting used when meeting someone. If you were referring to something else, please provide more context or check the spelling.
The word "hi" is a relatively modern greeting that originated in the 19th century, possibly as a form of the word "hey." It is informal and commonly used in everyday language.
If "hj" refers to a different word or idea, please clarify, and I would be happy to assist you further.