TikTok's focus is on videos that play on repeat until you go to the next video. (In this way, it's similar to an app called Vine, which Twitter bought and then discontinued.)
However, the emphasis on TikTok is on the audio that goes with each video.
I equate TikTok clips to audio-based memes.
Image-based memes tend to follow established formats that set up the joke. If you see the distracted boyfriend picture, you can guess that the meme's punchline will involve wanting something you shouldn't have.
It's the same idea on TikTok, except the music sets up a meme's foundation.
"YMCA" by the Village People, for example, is often used in videos that show people walking up to their relatives and then suddenly smacking them with something, such as a snowball. Yes, this meme's cruel. It's also pretty funny.