34% Attacks
From CryptoWiki
As discussed in this thread from a Cardano forum:
"There’s a whole separate family of consensus protocols called “33% resistant” which cannot resist 34% of adversarial control, e.g.: Algorand, Hyperledger, RSCoin, Casper (in asynchronous setting), Omniledger, etc.
Ouroboros is “50% resistant” (in synchronous setting) which automatically puts it into “34% resistant” group too So it was more like a note from Maki, that no one can do more than 1/2 yet, but at least it’s not 1/3"