Spenserian sonnets, which developed from Edmund Spenser's work "The Faerie Queen," are 14-line poems with the rhyme scheme ababbcbccdcdee. Usually, the first 12 lines develop three related ideas in quatrains, or four-line sections, while the last two lines create the volta, or "turn."
Spenserian sonnets are similar to the later Shakespearian sonnet, but have a tighter rhyme scheme. Both these sonnet forms use three quatrains finished with a couplet at the end that often comprises the volta, while the third sonnet form, the Petrarchan or Italian, uses an eight-line octave finished with a six-line sestet volta. Spenserian sonnets often indicate a false volta, starting line 9 with words like "But" or "Yet," then continuing with a third quatrain and delaying the true volta until the last two lines.
The volta is a conclusion that casts a fresh light on the ideas developed in the first part of the sonnet. For example, in Shakespeare's Sonnet 73, imagery of death and endings such as twilight, a dying fire, autumn leaves and a deathbed draw the reader's attention, while the last two lines warn the reader that because that ending awaits all, he should love now while he can. Spenserian sonnets usually delay the volta until the ending couplet, but Shakespearian sonnets sometimes begin the volta at line 9, creating a sestet volta.