A reply girl was a type of female YouTube user who uploaded video responses to popular YouTube videos, at a time when such responses were displayed prominently by the site.
In 2012, YouTube gave significant weight to video responses when suggesting further viewing for any given video, putting them "almost automatically" at the top of the list. Users known as "reply girls" realised that by responding to popular videos, such as those featured on the YouTube home page, their own content could receive a significant audience. By selecting a suggestive thumbnail for the response, often filmed in a push-up bra or low-cut top, posters could encourage viewers to click the image and view the video. Although many users would click the "dislike" link on the videos, this was taken by YouTube's algorithm as legitimate engagement, and the videos would be ranked more highly.
With YouTube rewarding users for large numbers of video views, reply girls were able to earn significant income by exploiting this aspect of the website. Megan Lee Heart, whose YouTube channel reached 38,000 subscribers and had over 47 million views at the time, made tens of thousands of dollars, claiming to have made $80,000 on her channel page description. Alejandra Gaitan was thought to be earning around a hundred dollars for each of the "short, rambling [and] usually pointless" videos that she posted, with some of the more popular ones raising close to $1000.
In March 2012, YouTube updated its algorithm to give less weight to suggested videos which were only watched briefly by users, announcing that the site would be "focusing more prominently on time watched". Gaitan expressed concern that this would "kill almost every reply channel", despite that being the stated intention of the action.