A Double Nickel in basketball refers to a player scoring 55 points in one game.
The term comes from the fact that a nickel is worth 5 cents. So, two nickels, or a "double nickel", represent the number 55. A double nickel is an impressive feat that few players have achieved. It requires a combination of skill, endurance, and a lot of shot attempts. Reaching a double nickel is celebrated as a milestone-scoring achievement in basketball.
Michael Jordan famously scored a double nickel against the New York Knicks in 1995.