BOT is a software application or software that runs automated tasks (scripts) over the internet or the blockchain. Typically, bots perform tasks that are both simple and structurally repetitive, at a much higher rate than would be possible for a human alone. The largest use of web spidering (web crawler), in which an automated script fetches, analyzes and files information from web servers at many times the speed of a human. On the internet, more than half of all web traffic is made up of bots.
In Steemit the most common of bots is for upvoting posts but there are other popular bots running on the platform. Bots exists in Steem Ecosystem since the official launch in July 4th, 2016, at that time the steemian 
A "bot" may differ slightly from a "script." Typically, a bot will watch for events For example, a bot could watch for a new post and vote on a script. This distinction becomes important because of a long period of time.
Bots can be simple or complex gold. A simple bot will take action only on a very limited set of conditions. For example, "if there's a new post, upvote it." More conditions create complexity. For example, "if there's a new post, upvote it on one has already voted on
List of Bots
https://www.steem.center/index.php?title=List_of_Bots