Burlesque can be defined as
an artistic composition, especially literary or dramatic, that, for the sake of laughter, vulgarizes lofty material or treats ordinary material with mock dignity.
Parody is defined as
a humorous or satirical imitation of a serious piece of literature or writing: his hilarious parody of Hamlet's soliloquy.
A parody is most often based on a work that was created with a sincere and serious intent. The parody follows the format of the original piece, using similar word patterns and elements wherever possible, but carries a completely different message that may make fun of the original content. Burlesque is more oriented toward emphasizing a humorous and often vulgar rendition of the original work, which may not be as lofty in original form as a piece that might be parodied. Burlesque is less refined than parody, making use of more bawdy language and imagery and treating the original with less respect than a parody.