Haiku (plural: haiku!):
a short (having no more than four lines) nature-oriented poem containing a reference to a certain season, or a kigo / season word, and consisting of two parts.
Hokku:
traditionally, a first stanza in renga.
Before Shiki, the name for what we now know as haiku.
Senryu:
a poem dealing with human affairs, usually written in the same form as haiku but without a kigo.
A single ant
gets a good girl
and as river-banks lie
man and wife
Sheltering from the rain,
the letters on the Buddha's forehead
I study hard!
Monoku:
a one-line haiku or senryu poem
Examples
autumn ilness the white noise of crickets
mosquitoes and young couples in love in another language
a wet-black boulder blue december sky
by Jim Kacian (first published in Shamrock Haiku Journal No 1)
Renga (linked verse):
a linked poems usually composed by two or more poets (5-7-5 and 7-7 onji).
Rensaku (linked work):
a bunch of haiku/tanka written around the same event/experience.
Gunsaku (group work):
a sequence of haiku/tanka written around the same event/experience.
Ginko:
a walk in the nature of a group of haiku poets.
Poems from the ginko organised by the Irish Haiku Society in 2007 can be viewed here:
http://irishhaiku2007.webs.com/poemsfromtheginko.htm
Photographs from the same ginko are available here:
http://irishhaiku.webs.com/ginko.htm