it is a software fork of the reference client. If 750 of the last 1000 rolling blocks mined are bip109 blocks then it will trigger the classic nodes to make up to 2mb blocks 28 days after that happens...if that happens then those who are still using bitcoin core (the reference client) will potentially run into trouble if blocks bigger than 1 MB (which is very likely to happen if a bip109 activates it will trigger a network fork). This is called a hard fork because it requires the nodes to all be rolled up to classic in order to work.
Just to make it clear, if it gets activated you can expect other Bitcoin clients to update the code to stay compatible with Bitcoin network. And it is true when somebody lives under a rock, his full node really might become incompatible. But it is always the risk with hard forks even when it come from Core or longer activation period.
Bitcoin Classic=waste of time!
That's all you need to know.
Most of the guys who lead this attempt of a hostile takeover are con artists, scammers, liars, heads with contact to alphabet agencies and drug addicts.
If you at least tried to unity Bitcoiners with some reasonable comment why voting for Classic is bad and doing nothing with 1MB is much better, not just divide Bitcoiners and declare different opinion as just a hostile takeover and whatever bad you just imagined in your FUD attempt.
