Pyran is a very simple molecule, similar to furan. It is a 6 member ring with the formula C5H5O. It looks something like this:
/ O \
/ \
/ \
H--/ \--H
|| ||
|| ||
/ \ / \
H \ / H
\ /
|
H
This molecule isn't particularly significant. Its main claim to fame is that its the basis for the naming of
pyranose carbohydrates, which are widely used in
biochemistry. As a 6-member
heterocycle, the compounds off which it is based can be slightly more stable than
furanoses. Ringed carbohydrates will prefer to align in this format first.