The acronym RTM has always been used by Microsoft as described in this Wikipedia article. There is absolutely no confusion here, according to the rules set by John we are guessing the Release To Manufacturing date.
No General Availability day, not the day when Gabe Aul tweets Windows 10 being available, not the day Gabe Aul tweets telling sorry we can't make that day I tweeted earlier but we'll do it on Thursday, not a self coined Never-Officially-Used-In-Any-Context-By-Microsoft-Or-Any-Other-Major-Player days like "release to market" (please Google it and check how official term that is) or any other "I Just Named a Day".
@Wolfgang, which date you want? Please make a post just containing one date, the day you will think is the RTM day. The one you picked for RTM in your earlier post is already taken.