A stanza is one “verse” of a poem, a group of lines separated by a space from the stanza before and/or after it. (Technically, the sections of a poem are called stanzas only if they have the same number of lines, the same rhyme scheme, and the same meter. If they don’t don’t match up like that, they’re called strophes. But many people ignore that distinction and use the word “stanza” in either case.) A sonnet is a 14-line poem in iambic pentameter with a particular rhyme scheme. There is more than one traditional sonnet rhyme scheme. You can web search “sonnet” for more details. The 14 lines of a sonnet are sometimes printed as one unit, with no spaces to divide the poem into separate sections. Sometimes a sonnet is divided into an octave and a sestet (groups of eight and six lines), sometimes into three quatrains (groups of four lines) and a final couplet (two lines). Even if a sonnet is divided up in any of those ways, the sections are not usually referred to as stanzas.
