A sonnet is simply another means to a creative, poetic end. It has a very distinct form. For example, the Elizabethan sonnet form (also referred to as the Shakespearean sonnet because of his vast contributions to the form) consists of fourteen lines. Of these fourteen, the first twelve are divided into three sets of four lines, called a quatrain. The last two lines are in the form of a couplet, a pair of rhyming lines.
Each of these lines will typically have ten syllables arranged in iambic pentameter. An iamb is two syllables, the first unaccented, the second receiving the stress. However, many writers in the sonnet form, Shakespeare included, strayed from strict iambic pentameter on occasion when it suited their purpose.
These lines will usually follow a very specific rhyme scheme, as well.
The first quatrain - abab
The second quatrain - cdcd
The third quatrain - efef
The final couplet - gg
A Shakespearean sonnet uses a basic thematic structure.
A sonnet is a poem that expresses a single, complete thought, idea, or sentiment. A sonnet must consist of 14 lines, usually in iambic pentameter (see below), with the rhymes arranged according to one of certain definite schemes.