[valtism]

The term signal was used, because RxJS had already taken the term "Observable" to refer to their primitives, which are actually more like streams.

Because of this, Ryan Carniato of SolidJS referred to his own observable primitives as "signals" and this has become the default terminology to talk about this type of pattern within the context of web development.

Really, signals should be thought of as a type of observable.