It's the automatic script google has coded that visits webpages and records data for google to use in their search engine. It's a good thing if it's on your forum.
"Googlebots" are usually effectivly spyware online. At scheduled periods, say once every day / week / month the crawlers are sent through almost every url link on any page observed. These bots scan the world wide web for new web pages, or updated pages then report back to be able to Google server which categorizes the web page by the text content.
Then it's assigned a lookup keyword(s) to that the site it produced correspond the key expression a user connected with Google may enter in.