Duplicated ("amplified") tiny fragments of RNA partially matching the reference sequence of Wu Flu, which coincidentally means you cannot distinguish it from the common flu
In essence you use reverse transcription to convert the RNA into double-stranded DNA, you separate it, add a primer that is allegedly specific DNA designed to only attach to the ostensibly "viral DNA". You repeat this a bunch of times until you have enough DNA copies so that you can say oh wow this allegedly specific DNA primer we used resulted in replication of the allegedly viral DNA so it must be the epic wu flu!
In reality, this is extremely untrustworthy and they have no idea what virus fragments were in your lil nostril