Unfortunately a very common mixup. Here is Erik Meijer (aka headinthebox), the main guy behind Rx, talking about the difference[1]:
Let's keep "FRP" for what it really stands for in honor of it's inventor (http://conal.net/talks/). Rx is not FRP and was explicitly designed as a discrete collection API on purpose (as opposed to continuous time varying values).
...
Let's keep "FRP" for what it really stands for in honor of it's inventor (http://conal.net/talks/). Rx is not FRP and was explicitly designed as a discrete collection API on purpose (as opposed to continuous time varying values). ...
[1] https://github.com/ReactiveX/reactivex.github.io/issues/130