I thought that they were the same thing for a while, but I often see phrasing in blogs or in answers here that seems to imply that there is a difference between the two. Even SO has two distinct tags, but their description doesn't show any clear difference.
I searched around for a bit and it only added to the confusion as it seems that I am not the only one who's unsure about what means what. Is there an official definition for both of these terms, perhaps defined by Ecma International themselves? If not, is there at least a commonly accepted definition?
As @JamesAllardice already said in the comments, the term harmony refers to all proposals for extending the current (ES5) language that meet the common goals of the TC39 committee.
Some of these harmony proposals are then selected and incorporated into the various specification drafts for the next version of the language (ES-next), which is currently ES6.
Those proposals that were not (yet) approved by the TC39 committee because of ongoing disputes ("disharmony") are called straw-man proposals.
来源：https://stackoverflow.com/questions/21580428/what-is-the-difference-between-ecmascript-6-and-ecmascript-harmony