Definition: Penalty Area

An area from which relief with a one-stroke penalty is allowed if the player's ball comes to rest there.

A penalty area is:

Any body of water on the course (whether or not marked by the Committee), including a sea, lake, pond, river, ditch, surface drainage ditch or other open watercourse (even if not containing water), and
Any other part of the course the Committee defines as a penalty area.

A penalty area is one of the five defined areas of the course.There are two different types of penalty areas, distinguished by the colour used to mark them:

Yellow penalty areas (marked with yellow lines or yellow stakes) give the player two relief options (Rules 17.1d(1) and (2)).
Red penalty areas (marked with red lines or red stakes) give the player an extra lateral relief option (Rule 17.1d(3)), in addition to the two relief options available for yellow penalty areas.

If the colour of a penalty area has not been marked or indicated by the Committee, it is treated as a red penalty area.The edge of a penalty area extends both up above the ground and down below the ground:

This means that all ground and anything else (such as any natural or artificial object) inside the edge is part of the penalty area, whether on, above or below the surface of the ground.
If an object is both inside and outside the edge (such as a bridge over the penalty area, or a tree rooted inside the edge with branches extending outside the edge or vice versa), only the part of the object that is inside the edge is part of the penalty area.

The edge of a penalty area should be defined by stakes, lines or physical features:

Stakes: When defined by stakes, the edge of the penalty area is defined by the line between the outside points of the stakes at ground level, and the stakes are inside the penalty area.
Lines: When defined by a painted line on the ground, the edge of the penalty area is the outside edge of the line, and the line itself is in the penalty area.
Physical Features: When defined by physical features (such as a beach or desert area or a retaining wall), the Committee should say how the edge of the penalty area is defined.

When the edge of a penalty area is defined by lines or by physical features, stakes may be used to show where the penalty area is located.

When stakes are used to define or show the edge of a penalty area, they are obstructions.

If a Committee has mistakenly excluded an area of water that is clearly part of a penalty area when defining its edge (such as by placing stakes in a location that means there is a portion of water from the penalty area that appears to be in the general area), that area is part of the penalty area.

When the edge of a body of water is not defined by the Committee, the edge of that penalty area is defined by its natural boundaries (that is, where the ground slopes down to form the depression that can hold the water).

If an open watercourse usually does not contain water (such as a drainage ditch or run-off area that is dry except during a rainy season), the Committee may define that area as part of the general area (which means it is not a penalty area).