Define suspicious birthdays

The Term suspicious birthdays is meaningless. What is so suspicious about it? Everybody has a birthday. It’s an incomplete thought. Percentiles make sense when you’re talking about height, weight, side of a physical characteristic, income. But percentile is meaningless. People with birthdays on January 1 are in the 0.3 percentile while people with birthdays on December 31 are in the 99.7 percentile