read "boozey", above. Complete, tight, punchy. Nice form on top of it.
I recall reading that the original intent of haiku was the use of metaphor, and allegory to illustrate rather than represent. "Rock...smooth" represents moving water. "Willow tree" indicates the movement of the wind; "cloud" refers to the process of burning, and so on. These commonly-used symbols generally refer to a seasonal element also ("willow tree" wouldn't appear in a poem about winter, etc.)
I think that technically, there is also a geographical element to haiku. If "cliffs" appears in a poem, it wouldn't be refering to an area of the country that doesn't have cliffs, like a desert. For example, if I'm writing a poem about New England, and use the word "Bluffs" it could only be refering to Block Island, Rhode Island not, say, New London, Conn from where I actually write this.