Altvacs
‘Altvac’ is short for ‘alternate vacation.’ It’s one of the things that you get when the concept of alternate timelines is first finally proven, then commercialized: people go find a timeline where they exist, only in a different life, and then they and their alternate selves swap timelines for a week or two. It’s considered rude to not tell anybody that you’re temporarily living your alternate self’s life, but it often happens, which can lead to some very interesting social situations. At least one media company films the most entertaining ones, for later commercial use.