What are zkSNARK parameters and how to verify them? When installing the zcash client for the first time it downlods a bulk of around 900 MiB in zkSNARK parameters. I am wondering: why and what are they exactly used for? Is this a security feature? How to verify the parameters?

What are zkSNARK parameters and how to verify them?
It's basically a zero knowledge proof that is easy to verify. The parameters are given on the zcash site. you can check it here
https://z.cash/blog/generating-zcash-parameters.html