The definition must have been in a chemistry book about the 11th grade. It’s the only positive thing I can recall about that wasted year-long class. Forgive my old-fashioned symbols. To me, X still means ‘times.’ It’s the symbol for multiplication. We were taught the asterisk * just means another exception to a rule, or Roger Maris hitting 61 home runs in a season against way better pitching isn’t the real record. It’s a symbol that means things are way more complicated than I thought. Great. That helps.