Head

The head of an animal is the anterior part that bears the mouth, the brain and various sensory organs (e.g. organs of sight, hearing, smell and taste). The very simplest animals do not have a head, but most bilaterally symmetric forms do. In vertebrates the contents of the head are protected by an enclosure of bone called the skull, which is attached to the spine.

Head is often a part of a title of office, meaning "the highest". A "head of department" is thus the person with the highest standing in said department. This use might stem from the fact that the head is the highest placed part of the human body, or from the fact that the brain and therefore cognitive functions and decision making is located in the head.

Example of a flower 'head (Larger version)

The term 'head' has a technical meaning in botany. A head is a type of inflorescence, previously known as a composite flower — a structure composed of numerous individual flowers. Species of plants of the Family Asteraceae typically have flower heads.

In fluid dynamics, head refers to the constant right hand side in the incompressible steady version of Bernoulli's equation. It is possible to express head in either meters or in Pascals (the SI unit of pressure).

This is best understood by considering a waterwheel: the head is the vertical distance from the waterwheel to the free surface of the millpond.

More generally, when considering a flow, one says that head is lost if energy is dissipated, usually through turbulence. In the context of steam trains, one talks of a good head of steam, referring to the pressure in the boiler.

Some dictionaries define close to thirty meanings of the word head. However, a majority of usages are associated with the connotation of forward, top, essential, control, etc., which are derived from attributes of an animal head (or brain). One of the few exceptions is that of the latrine of a marine vessel, which is called the head.

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