Definition

A definition is a statement of the meaning of a term (a word, phrase, or other set of symbols). Definitions can be classified into two large categories, intensional definitions (which try to give the essence of a term) and extensional definitions (which proceed by listing the objects that a term describes). Another important category of definitions is the class of ostensive definitions, which convey the meaning of a term by pointing out examples. A term may have many different senses and multiple meanings, and thus require multiple definitions.In mathematics, a definition is used to give a precise meaning to a new term, instead of describing a pre-existing term. Definitions and axioms are the basis on which all of modern mathematics is constructed.

Wikipedia

Definition (noun)
A statement of the meaning of a word or word group or a sign or symbol (dictionary definitions).
Definition (noun)
A statement expressing the essential nature of something; formulation
Definition (noun)
The action or process of defining.
Definition (noun)
The act of defining; determination of the limits.
Definition (noun)
A product of defining.
Definition (noun)
The action or power of describing, explaining, or making definite and clear.
"Her comic genius is beyond definition."
Definition (noun)
Clarity of visual presentation, distinctness of outline or detail.
"The definition of a telescope."
"Improve the definition of an image."
Definition (noun)
Clarity, especially of musical sound in reproduction.
Definition (noun)
Sharp demarcation of outlines or limits.
"A jacket with distinct waist definition."
Definition (noun)
The degree to which individual muscles are distinct on the body.
Definition (noun)
A statement which provides a previous declaration with a value or body of a subroutine (in the case of function).
Definition (noun)
A statement that establishes the referent of a term or notation.

Wiktionary

Definition (noun)
a statement of the exact meaning of a word, especially in a dictionary
"a dictionary definition of the verb"
Definition (noun)
an exact statement or description of the nature, scope, or meaning of something
"our definition of what constitutes poetry"
Definition (noun)
the action or process of defining something
"a question of definition"
"issues of methodology and definition"
Definition (noun)
the degree of distinctness in outline of an object, image, or sound
"the clarity and definition of pictures can be aided by using computer graphics"
Definition (noun)
the capacity of a device to make images distinct in outline
"we've been pleased with the definition of this TV"

Oxford Dictionary

Definition (noun)
The act of defining; determination of the limits; as, a telescope accurate in definition.
Definition (noun)
Act of ascertaining and explaining the signification; a description of a thing by its properties; an explanation of the meaning of a word or term; as, the definition of "circle;" the definition of "wit;" an exact definition; a loose definition.
Definition (noun)
Description; sort.
Definition (noun)
An exact enunciation of the constituents which make up the logical essence.
Definition (noun)
Distinctness or clearness, as of an image formed by an optical instrument; precision in detail.

Webster Dictionary

Definition (noun)
a concise explanation of the meaning of a word or phrase or symbol
Definition (noun)
clarity of outline;
"exercise had give his muscles superior definition"

Princeton's WordNet