Question

what is a stanza

Answer 1

A stanza is a group of lines in a poem.
http://www.merriam-webster.com/dictionary/stanza

For example, in the following poem http://www.bartleby.com/119/1.html
Each group of lines (5 lines in this case) is a stanza.

Answer 2

Like in a song, it's the verse. In a poem, it's the stanza. It's usually for 3, 4 or 5 lines.

Answer 3

It could be any number of lines. Depends on the type of poetry. In freeform poetry it could be 10, 20, even a few thousand lines. The Illiad and Odyssey are both poems. There are LOTS of lines per stanza.