# Technical definition

A technical definition is a definition in technical communication describing or explaining technical terminology. Technical definitions are used to introduce the vocabulary which makes communication in a particular field succinct and unambiguous. (For example, the iliac crest from medical terminology is the top ridge of the hip bone. (See ilium.))

## Types of technical definitions

There are three main types of technical definitions.[1]

1. Parenthetical definitions
2. Sentence definitions
3. Extended definitions

### Examples

Aniline, a benzene ring with an amine group, is a versatile chemical used in many organic syntheses.

The genus Helogale (dwarf mongooses) contains two species.

## Sentence definitions

These definitions generally appear in three different places: within the text, in margin notes, or in a glossary. Regardless of position in the document, most sentence definitions follow the basic form of term, category, and distinguishing features.

### Examples

A major scale is a diatonic scale which has the semitone interval pattern 2-2-1-2-2-2-1.

• term: major scale
• category: diatonic scales
• distinguishing features: semitone interval pattern 2-2-1-2-2-2-1

In mathematics, an abelian group is a group which is commutative.

• term: abelian group
• category: mathematical groups
• distinguishing features: commutative

## Extended definitions

When a term needs to be explained in great detail and precision, an extended definition is used. They can range in size from a few sentences to many pages. Shorter ones are usually found in the text, and lengthy definitions are placed in a glossary. Relatively complex concepts in mathematics require extended definitions in which mathematical objects are declared (e.g., let x be a real number...) and then restricted by conditions (often signaled by the phrase such that). These conditions often employ the universal and/or existential quantifiers (for all (${\displaystyle \forall }$), there exists (${\displaystyle \exists }$)).

Note: In mathematical definitions, convention dictates the use of the word if between the term to be defined and the definition; however, definitions should be interpreted as though if and only if were used in place of if.

### Examples

Definition of the limit of a single variable function:

Let ${\displaystyle f}$ be a real-valued function of a real variable and ${\displaystyle x}$, ${\displaystyle a}$, and ${\displaystyle L}$ be real numbers. We say that the limit of ${\displaystyle f}$ as ${\displaystyle x}$ approaches ${\displaystyle a}$ is ${\displaystyle L}$ (or, ${\displaystyle f(x)}$ tends to ${\displaystyle L}$ as ${\displaystyle x}$ approaches ${\displaystyle a}$) and write ${\textstyle \lim _{x\to a}f(x)=L}$ if, for all ${\displaystyle \epsilon >0}$, there exists ${\displaystyle \delta >0}$ such that whenever ${\displaystyle x}$ satisfies ${\displaystyle 0<|x-a|<\delta }$, the inequality ${\displaystyle |f(x)-L|<\epsilon }$ holds.

## References

1. ^ Johnson-Sheehan, R: "Technical Communication Today", pages 507-522. Pearson Longman, 2007