holes

A hole is an empty space or opening in a solid object, surface, or interface. Holes can be natural, such as a cavern or a pothole, or man-made, such as a drilled bore or a perforation. The term is often used loosely to describe any absence of material that creates an opening, cavity, or recess.

In materials and engineering, holes are often produced by drilling, punching, or wear, and they may function as fasteners, passageways for fluids, or ventilation.

In geometry and topology, holes are not physical gaps but features describing an object's connectivity. For example, a ring or torus has a hole through the center; topologists measure holes by genus or Betti numbers. A hole may be non-contractible, meaning it cannot be shrunk to a point without leaving the object.

Common natural holes include caves, boreholes, wells, and sinkholes; anthropogenic holes include drilled holes, pipes, chimneys, and manholes.

Holes are described by size and shape; diameter for circular holes, cross-section for non-circular; depth; tolerances; roughness interior. In porous materials, a collection of pores constitutes porosity; fluid flow depends on pore geometry.

Holes influence mechanical strength, fluid dynamics, acoustics, and thermal properties. They can be desirable (fasteners, vents) or problematic (structural flaws, leaks).