A pentomino is a geometric shape formed by connecting five equal squares edge to edge. There are 12 unique pentominoes, each with a different arrangement of squares. These shapes can be used in various puzzles and games, making them popular in recreational mathematics. Pentominoes can be arranged to fill a rectangle or other shapes without gaps or overlaps. They are often used in educational settings to teach concepts of geometry, spatial reasoning, and problem-solving. The study of pentominoes is related to topics like tessellation and combinatorial geometry.