Parody occurs when someone (most often legally) copies the style and/or elements of someone else’s creative work to make fun of it (and usually also celebrate it).
Harry Pothead parody
People often assume that parody is critical mode, but as the “Harry Pothead” example suggests it is frequently very mild-mannered and need not be critical of the original in any serious way.
Using parody is a double-edged sword if you actually want to criticize something or make people feel differently about it. The author Vladimir Nabokov once said “Satire is a lesson; parody is a game.” Like a game, parody usually is more a matter of fun than criticism, and parodies can actually serve to reinforce the values of what they are parodying by reproducing and re-legitimizing them. For instance, when Weird Al Yankovic parodies a popular song, it essentially adds to the song’s visibility and pervasiveness in culture and could even draw new listeners to a song they otherwise might not have listened to.
Be careful you don’t make another “ad” for something you want to attack.
See also culture jam, parody vs culture jam