To some of you, you may have just heard the subject in a announcer voice style or an image of "first blood" passed through your mind.
A "reference" is any element of any medium [speech, art, action, etc.] that makes 'reference' to any thing within geek-dom and its culture or society.
A poor definition by my standards but sufficient. Internet memes can be references, to ask someone about their liking of mudkips is a reference. To speak, only, three or four, words at, a time, [original star trek/shatner] is a reference. To randomly do a zombie dance followed by singing lines of the rick roll is a generic reference followed by a negative refer