What are vettable vs. non-vettable smart contracts?

I was reading some different crypto articles and have noticed a couple mentions about certain Ethereum smart contracts being "vettable" while others are "non-vettable". I am away from my main comp where i was reading and don't have a URL at the moment.

Does anyone know off-hand exactly what is meant by vettable vs. non-vettable smart contract?

Thanks