OTT or Over The Top is video programming transmitted via the Internet and bypassing traditional cable or broadcast distribution, and can be watched on any type of internet connected device.
CTV or Connected TV is that portion of the OTT universe that is viewed on an actual television set, usually through a streaming device like Roku or via a smart TV. OTT can be subscription supported (usually without ad, i.e. Netflix) or advertising supported (i.e. Hulu).