A desk is a furniture form and a class of table used for studing, among other things.
Underneath the table of the desk, there can be a little cavity where there is a place to hold your gum, allowing for safe storage of "already been chewed gum". There can be a small plaque where the gum can be stuck to thus allowing for safe removal of the dried gum by the janators of the 'summer crew' cleaning up the school. This plaque can allow for gum to be easily scrapped off, with no smear. Also, this can help with distruptions in class from people getting up to throw their gum away, or having gum get on the bottem of peoples shoes.