Usually this is someone who can single handed change the bitcoin price by setting long and shorts positions usually at different exchanges and therefor move the price of BTC more that 10 %

Ex 1) there are short positions on Bitmex that might expire of the amount of 100mUSD in a day and a Whale by moving the BTC price can "crash" those positions with a huge order that will render those positions worthless.

Simultaneously he might have other positions at other exchanges that will trigger the "bot" trading army to panic sell or buy.

Therefor a whale by definition is someone who can single handed make big "waves" on the price by making the price go up or down at will.

There are many thesis what amount a whale need to have in order to create those "waves" but in reality it is really how many sell/buy orders there are on the markse so that he can "trick" sellers with a fake "sell wall" and creating panic and simultaneously buy those who panic sell.

A famous Bitmex Whale is JOE007, you can find him on twitter.

Hope this clears some of the smoke

K44