Usually it's "something else" that turns into RJ45 (as ethernet has a maximum length) - now if you're in a datacenter you likely can get raw RJ45 Internet).
It's an old term used by telecom to refer to the phone they owned that's in the customers home. It has been used after by internet providers if they put a device in your home. If it's your own device it's not a CPE as seen from the isp perspective.