I guess that you are a new in this market. As far as I know that whales are people or also a group of people working together to gather large percentage  of that coin and can drag the coin price to the desired price. When the coin price gets decreased, most of users sell it with low, Whale will make use of this chance to buy many coins in low. In a nutshell, probably many people get scared of  Whale. If you are in this market for a long term, gradually you will understand more about Whale.