What's the difference between quatrain and sestet?

Quatrain

Definition:

• (n.) A stanza of four lines rhyming alternately.

Example Sentences:

Sestet

Definition:

• (n.) A piece of music composed for six voices or six instruments; a sextet; -- called also sestuor.
• (n.) The last six lines of a sonnet.

Example Sentences:

• (1) Sonnets, one should note in passing, are hard to read – particularly as they move on to the “sestet”, or last six lines.