A Roku smart TV is a combination of a smart TV and a Roku streaming device (also called an external media streamer).
A Beginner's Guide to Roku Players and Roku TVs – Price, How Rokus Work, and What to Expect
This combination combines traditional TV functions with an operating system/platform. This allows viewers to access, manage and view Internet and network-based media content directly from their TV set, without additional devices.
A Roku streaming stick is a separate, portable device that communicates wirelessly with a television to connect you to entertainment from the internet. A Roku TV, on the other hand, encompasses everything in the television.
Roku licenses its streaming platform for use in smart TVs. This means that Roku doesn’t make its own TVs, but manufacturers are allowed to incorporate Roku features into their TVs.