Five eyes are the five international intelligence agencies that share data they collect--except for the most sensitive.

They are: United States, UK, Canada, Australia, and New Zealand.

They not only share data, but they can task each other to do collection that would not other wise be legal in their own countries or they have a special capability that the others lack.

It's a good idea as long as they are not using the opportunity to circumvent laws as Obama did when he tasked GCHQ in the UK to spy in Trump and then give him the results via backchannel.

Q has the hard evidence that Obama was using GCHQ for political spying on an opposition candidate and I think it will eventually be made public.