What is "dramatic irony"? How are Romeo's words an example of dramatic irony? Be specific!

Dramatic irony is a speech or a situation within a play, in which the audience is aware of what's going on, but the characters themselves are not.

The irony in Romeo's words can be found in the fact that he describes a dream in which Juliet finds him dead but awakens him with a kiss. Little does he know that it is Juliet, who is laying cold and is believed to be dead......

Another example of dramatic irony is when Romeo enters Juliet's tomb and he says, 'Is crimson in thy lips and not thy cheeks?', Romeo wonders why Juliet does not yet look dead however the audience knows that she is not dead but under the influence of a sleeping draught.