A whale is a person that have plenty of a particular currency. For example a bitcoin whale is a person that have alot of bitcoin. It must be 1000btc and above to qualify as a whale. Price can be manipulated my a whale when they dump some of their bag which make people  to think that the price is dropping and cause people  to panic sell and they will buy back the dip and acquire  more btc. The can also pump the price by buying more of btc for example and people  will think  the price is pumping  and they will FOMO ( fear of missing Out)  the whale will dump on them and take profit.