"Whale" is the colloquial term for someone who holds (or hodls) large amounts of digital assets. A whale tends not to trade often, but when they do, the transactions they make tend to be large-volume, having statistically significant influences on the volatility of the digital asset that they either traded or moved from a wallet to an exchange. For a time, "whale" referred mostly to people who hold large amounts of bitcoin; however, in 2019, a study published by the blockchain research firm Chainalysis revealed that one-third of the total supply of Ether, the native cryptocurrency of the Ethereum platform, was held by just 376 people worldwide.
Tracking whale behavior has sparked the creation of dedicated entities that monitor major blockchains and provide both public and private reports of large transactions. TokenAnalyst and WhaleAlert are two of the best known services. 
- The Bitcoin Whales: 1,000 People Who Own 40 Percent of the Market. Bloomberg.
- Just 376 People Found to Own a Third of All Ether Cryptocurrency. Bloomberg.
- Is This Behind The Latest $25 Billion Bitcoin And Crypto Price Rally?. Forbes.
- Website. TokenAnalyst.
- Website. WhaleAlert.