A like button, like option, or recommend button is a feature in communication software such as social networking services, Internet forums, news websites and blogs where the user can express that they like, enjoy or support certain content. Internet services that feature like buttons usually display the number of users who liked each content, and may show a full or partial list of them. This is a quantitative alternative to other methods of expressing reaction to content, like writing a reply text. Some websites also include a dislike button, so the user can either vote in favour, against or neutrally. Other websites include more complex Web content voting systems, for example five stars or reaction buttons to show a wider range of emotion to the content.
The first like button was created in 2005 at Vimeo, with a team comprising Andrew Pile, Jake Lodwick, Kunal Shah, and Zach Klein. It was meant to be a more casual alternative to "favorites", and was heavily inspired by "diggs" from the site Digg.com.
The like button was first announced as a FriendFeed feature on October 30, 2007 and was popularized within that community. Later the feature was integrated into Facebook before FriendFeed was acquired by Facebook August 10, 2009.
The Facebook like button is designed as a hand giving "thumbs up". It was originally discussed to have been a star or a plus sign, and during development the feature was referred to as "awesome" instead of "like".It was introduced on 9 February 2009. During May 2016, Facebook introduced reactions - a new way to express peoples emotions to Facebook posts. Some reactions included "Love", "Haha", "Wow", "Sad", or "Angry".
In 2010, as part of a wider redesign of the service, YouTube switched from a star-based rating system to Like/Dislike buttons. Under the previous system, users could rate videos on a scale from 1 to 5 stars; YouTube staff argued that this change reflected common usage of the system, as 2-, 3-, and 4-star ratings were not used as often.
In 2012, YouTube briefly experimented with replacing the Like and Dislike buttons with a Google+ +1 button.
In 2019, after the backlash from YouTube Rewind 2018, YouTube is now considering options to combat "dislike mobs," including an option to completely remove the dislike button. The video is the most disliked video on YouTube, passing Justin Bieber's "Baby".
In contrast to the display of the views, the display of the number of likes and dislikes on a YouTube video is normally not “frozen”, though rarely it can be frozen for unknown reasons. For example, on January 23, 2019, the likes and dislikes on Despacito were frozen for about 8 hours.   The glitch was fixed by 16:00 UTC that same day. 
On Reddit (a system of message boards), users can upvote and downvote posts (and comments on posts). The votes contribute to posters' and commenters' "karma" (Reddit's name for a user's overall rating).
Alongside "retweets", Twitter users could "favorite" posts made on the service, indicated by a gold star symbol ( ). In November 2015, to alleviate user confusion and put the function more in line with other social networks, the "favorite" function was renamed "like", and its button was changed from a star symbol to a heart ( ).
VK like buttons for posts, comments, media and external sites operate in a different way from Facebook. Liked content doesn't get automatically pushed to the user's wall, but is saved in the (private) Favorites section instead.
Instagram like button is indicated by a heart symbol, users could use the like button by double tapping on a post they like and there is no limit to number of posts they want to double tap. In July 2019, Instagram conducted a test of hiding a number of likes on users posts from followers, meaning that users can see the count of likes but not their followers.
In 2017, a man was fined 4,000 Swiss francs by a Swiss regional court for liking defamatory messages on Facebook written by other people which criticized an activist. According to the court, the defendant "clearly endorsed the unseemly content and made it his own".
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- Man fined by Swiss court for 'liking' defamatory comments on Facebook - The Guardian / AFP, 20 May 2017