A burlesque is a work that takes a relatively high subject and treats it in a relatively low fashion.
Example: Dryden’s Mac Flecknoe
Even though Mac Flecknoe is primarily a mock heroic, it has elements of burlesque within it, such as in Line 139. “Heavens bless my son, from Ireland let him reign/To far Badbadoes on the western main…” They are taking the relatively high subject of reign and royalty, but treating it in a relatively low fashion by essentially saying that the empire Shadwell reigns over is vast but empty. The proclamation, which should be taken seriously, is only used to draw attention to Shadwell’s failings in a humorous way.
Another example of burlesque is in Swift’s A Modest Proposal, where he takes the serious issue of overpopulation and puts it in a satire.