Out of Bounds (OB)
The area outside the legal boundaries of the course, marked with white stakes, hitting a ball there costs stroke and distance.
The stroke-and-distance penalty was formalized by the R&A at St. Andrews in the mid-1800s, with formal boundary definitions refined through 1886 and 1899. White stakes became the standardized way to mark the boundary over the 20th century, chosen to be visually distinct from the red and yellow stakes used for penalty areas.