A whale is a person or party that owns a large portion of a particular cryptocurrency.
There is no fixed amount that indicates whether someone is a whale or not. A whale is usually spoken of when this person or party has enough coins to influence the price of a cryptocurrency. To influence the price of Bitcoin, hundreds of millions or even billions are needed. This is why investment funds are also often seen as whales. Lesser-known currencies with a lower market cap require less money to influence the price.
The name “whale” is used because a whale is the largest animal on Earth. In the casino, this term is also used to refer to a player who has a lot of money. In crypto, other sea life is also used to indicate how much someone's share in a cryptocurrency is. For example, people talk about a shrimp for someone with a small share and a dolphin for a wallet with a medium share.
