Penguin proof backlinks is a term used by some SEO agencies and SEO tools to claim that the links they create for their clients will stay below the Google’s radar and will not be considered as low quality backlinks or even toxic backlinks.
Google’s Penguin algorithm updates are allowing the search engine to detect artificial links and link schemes that violate Google’s Webmaster Guidelines and to take sanctions by degrading SERP rankings.
Only natural link buiding can be really considered as Penguin proof. There is no garantuee for artificial linking, although it might be supposed that some smart and manual black hat practices are actually Penguin-proof. Nevertheless there is the best chance that big backlink blasts are not Penguin proof.
An example of "penguin-proof" backlinks offer: