What is one feature of the sonnet form?

The most general form of a Sonnet is a poem of 14 lines, written iambic pentameter, or in some continental styles the meter may be hendecasyllable or the Alexandriene meter. However there are two specific forms of sonnets which have a certain structure, these are the Petrachan (or Italian) Sonnet and the Shakespearean Sonnet.

These two styles generally employ a specific rhyme scheme. in the Shakespearean sonnet the rhyme scheme is usually A-B-A-B C-D-C-D E-F-E-F G-G. wheras the Italian Sonnets are usually written in a rhyme scheme A-B-B-A A-B-B-A (for the sestet there were two different rhyming possibilities) C-D-E-C-D-E or C-D-C-C-D-C.

There is one other major form of English Sonnet, this was the Spencerian (named after the poet Edmund Spencer) Sonnet which had a different rhyme scheme again. It followed A-B-A-B B-C-B-C C-D-C-D E-E.