Yelpers sometimes organize their own meet-ups and events which aren't sponsored or endorsed by Yelp (though they are still promoted on Yelp for other Yelpers). This type of event is called an Unofficial Yelp Event, or UYE. If you put one of these shindigs on, please try to promote it as a UYE since it won't necessarily have Yelp's seal of approval.
Please also note that the experience you have at a venue hosting a UYE may not resemble the experience you'd have if you were attending as a regular customer. As a result, you shouldn't post a review about the venue unless you're describing your experience as a regular customer. If you want to post a review anyway, please post it on the relevant Yelp Event page rather than the business page.