“Whale” labels the high-spending tail of a game’s payer base. The skew is real and matters for analysis: it inflates variance, which makes monetization A/B tests need far larger samples than conversion tests.
The metaphor can mislead product decisions, though. Top spenders are usually a stage players reach through investment in the game, not a fixed species to be hunted. Designing for the journey into deeper engagement tends to work better than designing for the label.