Equal numbers of both sexes attend, usually paying a gratuity of around GBP£20. Each spends about three minutes talking to each member of the oppposite sex - the social interaction that takes place therein is referred to as a 'speed date'.
At the end of the evening everyone marks on a card who they would like to date again and who they wouldn't. The organisers then swap contact information between matches - usually an email address or mobile phone number.
Speed dating apparently started in New York, and was popularised by TV show 'Sex In The City'. It is now most popular amongst professionals in their mid 20's and 30's.