Gruyère cheese is a cow's milk cheese from France or Switzerland; the Swiss variant is called Greyerzer. It is firm to hard, and has excellent melting and toasting properties. Stronger-flavored than generic "Swiss cheese", Jarlsberg cheese, or Emmental cheese, it still has a pleasant nutlike taste. The authentic cheese is a light tan or yellow, with a distinct rind.
An American product, "creme de gruyere", has very little similarity to the true cheese. Typically wrapped in aluminium foil, this variant does appear to have gruyere flavoring, diluted with milk solids to make it into a soft, mildly flavored preparation.