Here is a good video explaining how this audio illusion works. The gist is there are two words mixed (overlapped) into the same time period, the word ‘Laurel’ is in the lower frequencies while the word ‘Yanny’ is in the upper frequencies.
By equalising away the lower or upper frequencies, you should be able to hear one or the other.
As mentioned before, the theory what word you hear is a indication of your hearing. The reason why this video turned viral is because you can be playing this same track over and over again to a group of friends, and some will hear ‘Laurel’, some ‘Yanny’ and then some who seem to hear a mixture or two.
You can also be hearing one word now, and the other later! You may even hear both! And this is why this video has gone viral.
So how could that be? The answer is not frequency hearing loss, it’s actually audio cognition.