Difference between UnityScript and JavaScript?

I am confused.

I just read for the first time that Unity supports this language called UnityScript which is built upon the ECMA standard (?). I’ve never heard of this language before, and it seems the people at Unity themselves aren’t shouting it from the rooftops: in the script reference for example, there is only a single mention of “UnityScript”.

Even so, it’s mentioned a lot of times on the community support sites and there seem to be special editors for UnityScript, like this one.

Can somebody please explain where the difference between UnityScript and JavaScript lies?
Is Unity just sloppily omitting the name of the not so popular language, when they publish “JavaScript” code snippets in the documentation?

I am by the way not a hard core programmer, but I do write both JavaScript and C# code for Unity.

Thank you!

Unityscript and Javascript are essentially different languages; it’s mostly a marketing move to call it “Javascript” in Unity. Some of the differences can be found here and here.