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
       \ /

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.