Question

The line “I wandered lonely as a cloud” is an example of

Answer 1

http://www.poemhunter.com/poem/i-wandered-lonely-as-a-cloud/

The first line of a famous poem.

It's in iambic tetrameter:
http://library.thinkquest.org/27864/data/cyoc/poetry.html

Answer 2

It is also an example of a simile... The poet is saying that he is as lonely as a sole cloud in a huge sky.