thumb|A small man-made garden pond at the Taj Lake Palace in Udaipur, India

A pond is a body of water smaller than a lake, both being examples of terrain features. Although the term pond is universally used to describe waterbodies that are smaller than lakes, an internationally recognised size cutoff has not yet been agreed, with values ranging from 2 hectares (20,000 m²) to 8 hectares (80,000 m²) used to distinguish the smaller from the larger waterbody.

In the United Kingdom, where the charity Pond Conservation has made some of the most extensive studies of ponds, the now widely adopted definition of a pond is 'A man-made or natural waterbody which is between 1 m² and 2 hectares (~5 acres or 20,000 m²) in area, which holds water for four months of the year or more'.

In other parts of Europe some biologists prefer to set the upper size limit at 5 ha (12.355 acres), and in North America even larger waterbodies are often called ponds. For example, Walden Pond in Concord, Massachusetts measures 62 acres. The international Ramsar wetland convention sets the upper size limit for ponds as 8 ha (19.768 acres). Although the size cutoff between ponds and lakes is partly subjective both are formed by ponding (standing) water.

Ponds may be man-made or natural in origin and can be made by excavating a hollow in which water may lie, filling an existing depression with ground or surface water or by retaining water from a stream, or by forming a dam to impound the water in a valley. Ponds can be made by a very wide range of natural processes, although in many parts of the world these are now severely constrained by human activity. In some countries backyardponds or garden ponds are popular and common. Many man-made ponds are used by hobbyists to keep fish and aquatic plants.

The techniques may be combined to form a reservoir in flat country by enclosing an area with an embankment. Such a pond, unless very small, is usually called a reservoir. In some cultures, the meaning has been extended to include small bodies of water impounded naturally.

There are many different definitions traditionally applied by freshwater biologists to ponds, such as:

• a body of water where light penetrates to the bottom of the waterbody
• a waterbody shallow enough for rooted water plants to grow throughout its area
• a waterbody which lacks wave action on the shoreline

Many of these definitions are very difficult to apply in practice, and may vary according to season, pollution or the presence of trees around the waterbody. For example, when a pond is too heavily shaded by trees for plants to grow throughout, does it cease to be a pond? If the waterbody is polluted, light may be prevented from penetrating to the bottom of even quite shallow ponds by dense blooms of algae - and if so, is the waterbody still a pond?