Reef tank = aquarium with live rock, corals and (usually but not always) fish, invertebrates.
Reef Ready = manufacturer term for a tank that's drilled and includes a built-in overflow. Depending on the brand it may or may not come with an 'overflow kit' (plumbing & bulkheads that fit inside the overflow).
I highly recommend a RR tank over a standard, non-drilled tank (unless you want to drill your own) - making the switch from sumpless to RR was the best thing I ever did. Everything is so much easier, the tank is more stable, all the equipment is hidden, and water changes are a breeze (the fish don't even know anything is happening - water changes in the sump = zero fish stress).