Hello there! ​ Polygon is a side chain. I’m not sure i can explain better than this... So i just refer you to what I've read some time ago. ​ https://www.web3.university/article/sidechains-vs-layer2s ​ Hope that helps 😉

Polygon is both a sidechain and a Layer 2. This is because Polygon stores data as if it's a standalone blockchain (sidechain), however it also writes checkpoints back to Ethereum to ensure a level of synchronization (L2). ​ I mentioned compared to rollups here: https://curious.xyz/questions/490 ​ ​