Definition of guano. : a fertilizer containing the accumulated excrement of seabirds or bats; broadly : excrement especially of seabirds or bats.
This is a cross section through the small intestine. The tall, vertical cells seen at the top of the tissue are columnar cells (one is shown - red arrow), which make up simple columnar epithelium (the cells at the bottom of the image are connective tissue, which will be discussed later). Since columnar cells are quite thick, they do not readily allow passive diffusion.
Squamous cells are flat and scale-like; cuboidal cells are cube shaped; and columnar cells are tall and rectangular, like the columns of a building. So, with that said, I'm sure you are wondering how pseudostratified columnar epithelium fit into this classification structure.