Stanzas can be defined as groups of lines, sometimes referred to (less precisely) as verses. Poems can be broken up into stanzas which usually share common features such as length, rhyme or rhythm.
Stanzas can also be irregular, and have no regular rhyming patterns to speak of.
The word 'stanza' derives from the Italian for room. Some stanzas have precise names. A Tercet is three lines long, and a Quatrain is four lines long. Stanzas of five, six, seven and eight lines are referred to as Quintrain, Sestet, Septet and Octave or Octet respectively.